diff --git a/ShipEngine/Models/ShipEngineException.cs b/ShipEngine/Models/ShipEngineException.cs
index 6d687e0a..b58bae78 100644
--- a/ShipEngine/Models/ShipEngineException.cs
+++ b/ShipEngine/Models/ShipEngineException.cs
@@ -1,6 +1,7 @@
 #pragma warning disable 1591
 
 using System;
+using System.Net.Http;
 
 namespace ShipEngineSDK
 {
@@ -32,18 +33,21 @@ public class ShipEngineException : Exception
         /// </summary>
         public ErrorCode ErrorCode { get; set; }
 
+        public HttpResponseMessage? Response { get; set; }
 
         public ShipEngineException(
             string message,
             ErrorSource errorSource = ErrorSource.Shipengine,
             ErrorType errorType = ErrorType.System,
             ErrorCode errorCode = ErrorCode.Unspecified,
-            string requestID = null) : base(message)
+            HttpResponseMessage? response = null,
+            string? requestId = null) : base(message)
         {
             ErrorSource = errorSource;
             ErrorType = errorType;
             ErrorCode = errorCode;
-            RequestId = requestID;
+            Response = response;
+            RequestId = requestId;
         }
     }
 }
\ No newline at end of file
diff --git a/ShipEngine/ShipEngine.cs b/ShipEngine/ShipEngine.cs
index 4b9f6ad7..818cebd7 100644
--- a/ShipEngine/ShipEngine.cs
+++ b/ShipEngine/ShipEngine.cs
@@ -1,6 +1,8 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using ShipEngineSDK.Common;
+using ShipEngineSDK.Manifests;
+using Result = ShipEngineSDK.ValidateAddresses.Result;
 using System;
 using System.Collections.Generic;
 using System.Net.Http;
@@ -9,14 +11,23 @@
 
 namespace ShipEngineSDK
 {
+    /// <summary>
+    /// Extension method to allow customized client configuration
+    /// </summary>
     public static class ShipEngineExtensions
     {
+        /// <summary>
+        /// Adds ShipEngine to the host builder and configures the client.
+        /// </summary>
+        /// <param name="builder"></param>
+        /// <param name="configureClient"></param>
+        /// <returns></returns>
         public static IHostApplicationBuilder AddShipEngine(this IHostApplicationBuilder builder, Action<HttpClient>? configureClient = null)
         {
             builder.Services.AddHttpClient<ShipEngine>(c =>
             {
                 var baseUri = builder.Configuration["ShipEngine:BaseUrl"] ?? "https://api.shipengine.com";
-                var apiKey = builder.Configuration["ShipEngine:ApiKey"];
+                var apiKey = builder.Configuration["ShipEngine:ApiKey"] ?? "";
                 ShipEngineClient.ConfigureHttpClient(c, apiKey, new Uri(baseUri));
                 configureClient?.Invoke(c);
             });
@@ -28,16 +39,18 @@ public static IHostApplicationBuilder AddShipEngine(this IHostApplicationBuilder
     /// <summary>
     /// Contains methods for interacting with the ShipEngine API.
     /// </summary>
-    public class ShipEngine : ShipEngineClient, IDisposable
+    public class ShipEngine : ShipEngineClient, IDisposable, IShipEngine
     {
         /// <summary>
         /// Global HttpClient for ShipEngine instance.
         /// </summary>
+        // ReSharper disable once InconsistentNaming
         public HttpClient _client;
 
         /// <summary>
         /// Global config for ShipEngine instance.
         /// </summary>
+        // ReSharper disable once InconsistentNaming
         public Config _config;
 
         /// <summary>
@@ -69,14 +82,23 @@ public ShipEngine(HttpClient httpClient) : base()
             _client = httpClient;
         }
 
-        // <summary>
-        // Dispose of the ShipEngine client
-        // </summary>
+        /// <summary>
+        /// Dispose of the ShipEngine client
+        /// </summary>
         public void Dispose()
         {
             _client.Dispose();
         }
 
+        /// <summary>
+        /// Modify the ShipEngine request
+        /// </summary>
+        public new ShipEngine ModifyRequest(Action<HttpRequestMessage> modifyRequest)
+        {
+            base.ModifyRequest = modifyRequest;
+            return this;
+        }
+
         /// <summary>
         /// Validates an address in nearly any country in the world.
         /// </summary>
@@ -398,4 +420,341 @@ public void Dispose()
             return labelResult;
         }
     }
+
+    /// <summary>
+    /// Mock implementation of IShipEngine
+    /// </summary>
+    public class ShipEngineMock : IShipEngine
+    {
+        /// <summary>
+        /// Validates an address in nearly any country in the world.
+        /// </summary>
+        /// <param name="addresses">The address to validate. This can even be an incomplete or improperly formatted address</param>
+        /// <returns>An address validation result object</returns>
+        public virtual Task<List<Result>> ValidateAddresses(List<Address> addresses)
+        {
+            return Task.FromResult(new List<Result>());
+        }
+
+        /// <summary>
+        /// Validates an address in nearly any country in the world.
+        /// </summary>
+        /// <param name="addresses">The address to validate. This can even be an incomplete or improperly formatted address</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call.</param>
+        /// <returns>An address validation result object</returns>
+        public virtual Task<List<Result>> ValidateAddresses(List<Address> addresses, Config methodConfig)
+        {
+            return Task.FromResult(new List<Result>());
+        }
+
+        /// <summary>
+        /// Retrieve a list of all carriers that have been added to this account
+        /// </summary>
+        /// <returns>A list of carriers</returns>
+        public virtual Task<ListCarriers.Result> ListCarriers()
+        {
+            return Task.FromResult(new ListCarriers.Result());
+        }
+
+        /// <summary>
+        /// Retrieve a list of all carriers that have been added to this account
+        /// </summary>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call.</param>
+        /// <returns>A list of carriers</returns>
+        public virtual Task<ListCarriers.Result> ListCarriers(Config methodConfig)
+        {
+            return Task.FromResult(new ListCarriers.Result());
+        }
+
+        /// <summary>
+        /// Create a manifest
+        /// </summary>
+        /// <param name="manifestParams">The details of the manifest you want to create.</param>
+        /// <returns></returns>
+        public virtual Task<Manifests.Result> CreateManifest(Params manifestParams)
+        {
+            return Task.FromResult(new Manifests.Result());
+        }
+
+        /// <summary>
+        /// Create a manifest
+        /// </summary>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call.</param>
+        /// <param name="manifestParams">The details of the manifest you want to create.</param>
+        /// <returns></returns>
+        public virtual Task<Manifests.Result> CreateManifest(Config methodConfig, Params manifestParams)
+        {
+            return Task.FromResult(new Manifests.Result());
+        }
+
+        /// <summary>
+        /// Void a label by ID to get a refund.
+        /// </summary>
+        /// <param name="labelId">The id of the label to void</param>
+        /// <returns>Result object indicating the success of the void label attempt</returns>
+        public virtual Task<VoidLabelWithLabelId.Result> VoidLabelWithLabelId(string labelId)
+        {
+            return Task.FromResult(new VoidLabelWithLabelId.Result());
+        }
+
+        /// <summary>
+        /// Void a label by ID to get a refund.
+        /// </summary>
+        /// <param name="labelId">The id of the label to void</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>Result object indicating the success of the void label attempt</returns>
+        public virtual Task<VoidLabelWithLabelId.Result> VoidLabelWithLabelId(string labelId, Config methodConfig)
+        {
+            return Task.FromResult(new VoidLabelWithLabelId.Result());
+        }
+
+        /// <summary>
+        /// Track a shipment using the label id
+        /// </summary>
+        /// <param name="labelId">The label id associated with the shipment</param>
+        /// <returns>An object that contains the label id tracking information</returns>
+        public virtual Task<TrackUsingLabelId.Result> TrackUsingLabelId(string labelId)
+        {
+            return Task.FromResult(new TrackUsingLabelId.Result());
+        }
+
+        /// <summary>
+        /// Track a shipment using the label id
+        /// </summary>
+        /// <param name="labelId">The label id associated with the shipment</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>An object that contains the label id tracking information</returns>
+        public virtual Task<TrackUsingLabelId.Result> TrackUsingLabelId(string labelId, Config methodConfig)
+        {
+            return Task.FromResult(new TrackUsingLabelId.Result());
+        }
+
+        /// <summary>
+        /// Tracks a package based on the trackingNumber and carrierCode.
+        /// </summary>
+        /// <param name="trackingNumber">The tracking number of the package you wish to track.</param>
+        /// <param name="carrierCode">The carrierCode for the trackingNumber you are using to track the package.</param>
+        /// <returns></returns>
+        public virtual Task<TrackUsingCarrierCodeAndTrackingNumber.Result> TrackUsingCarrierCodeAndTrackingNumber(string trackingNumber, string carrierCode)
+        {
+            return Task.FromResult(new TrackUsingCarrierCodeAndTrackingNumber.Result());
+        }
+
+        /// <summary>
+        /// Tracks a package based on the trackingNumber and carrierCode.
+        /// </summary>
+        /// <param name="trackingNumber">The tracking number of the package you wish to track.</param>
+        /// <param name="carrierCode">The carrierCode for the trackingNumber you are using to track the package.</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns></returns>
+        public virtual Task<TrackUsingCarrierCodeAndTrackingNumber.Result> TrackUsingCarrierCodeAndTrackingNumber(string trackingNumber, string carrierCode, Config methodConfig)
+        {
+            return Task.FromResult(new TrackUsingCarrierCodeAndTrackingNumber.Result());
+        }
+
+        /// <summary>
+        /// Create a label from shipment details
+        /// </summary>
+        /// <param name="labelParams">Details of the label that you want to create</param>
+        /// <returns>Object containing the created label information</returns>
+        public virtual Task<CreateLabelFromShipmentDetails.Result> CreateLabelFromShipmentDetails(CreateLabelFromShipmentDetails.Params labelParams)
+        {
+            return Task.FromResult(new CreateLabelFromShipmentDetails.Result());
+        }
+
+        /// <summary>
+        /// Create a label from shipment details
+        /// </summary>
+        /// <param name="labelParams">Details of the label that you want to create</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>Object containing the created label information</returns>
+        public virtual Task<CreateLabelFromShipmentDetails.Result> CreateLabelFromShipmentDetails(CreateLabelFromShipmentDetails.Params labelParams, Config methodConfig)
+        {
+            return Task.FromResult(new CreateLabelFromShipmentDetails.Result());
+        }
+
+        /// <summary>
+        /// Create a label from a rate id
+        /// </summary>
+        /// <param name="createLabelFromRateParams">The details of the rate that you want to use to purchase a label</param>
+        /// <returns>Object containing the created label information</returns>
+        public virtual Task<CreateLabelFromRate.Result> CreateLabelFromRate(CreateLabelFromRate.Params createLabelFromRateParams)
+        {
+            return Task.FromResult(new CreateLabelFromRate.Result());
+        }
+
+        /// <summary>
+        /// Create a label from a rate id
+        /// </summary>
+        /// <param name="createLabelFromRateParams">The details of the rate that you want to use to purchase a label</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>Object containing the created label information</returns>
+        public virtual Task<CreateLabelFromRate.Result> CreateLabelFromRate(CreateLabelFromRate.Params createLabelFromRateParams, Config methodConfig)
+        {
+            return Task.FromResult(new CreateLabelFromRate.Result());
+        }
+
+        /// <summary>
+        /// Retrieve rates for a package with the provided shipment details.
+        /// </summary>
+        /// <param name="rateParams"></param>
+        /// <returns>The rates result</returns>
+        public virtual Task<GetRatesWithShipmentDetails.Result> GetRatesWithShipmentDetails(GetRatesWithShipmentDetails.Params rateParams)
+        {
+            return Task.FromResult(new GetRatesWithShipmentDetails.Result());
+        }
+
+        /// <summary>
+        /// Retrieve rates for a package with the provided shipment details.
+        /// </summary>
+        /// <param name="rateParams"></param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>The rates result</returns>
+        public virtual Task<GetRatesWithShipmentDetails.Result> GetRatesWithShipmentDetails(GetRatesWithShipmentDetails.Params rateParams, Config methodConfig)
+        {
+            return Task.FromResult(new GetRatesWithShipmentDetails.Result());
+        }
+    }
+
+
+    /// <summary>
+    /// Interface for ShipEngine
+    /// </summary>
+    public interface IShipEngine
+    {
+        /// <summary>
+        /// Validates an address in nearly any country in the world.
+        /// </summary>
+        /// <param name="addresses">The address to validate. This can even be an incomplete or improperly formatted address</param>
+        /// <returns>An address validation result object</returns>
+        Task<List<ValidateAddresses.Result>> ValidateAddresses(List<Address> addresses);
+
+        /// <summary>
+        /// Validates an address in nearly any country in the world.
+        /// </summary>
+        /// <param name="addresses">The address to validate. This can even be an incomplete or improperly formatted address</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>An address validation result object</returns>
+        Task<List<ValidateAddresses.Result>> ValidateAddresses(List<Address> addresses, Config methodConfig);
+
+        /// <summary>
+        /// Retrieve a list of all carriers that have been added to this account
+        /// </summary>
+        /// <returns>A list of carriers</returns>
+        Task<ListCarriers.Result> ListCarriers();
+
+        /// <summary>
+        /// Retrieve a list of all carriers that have been added to this account
+        /// </summary>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call.</param>
+        /// <returns>A list of carriers</returns>
+        Task<ListCarriers.Result> ListCarriers(Config methodConfig);
+
+        /// <summary>
+        /// Create a manifest
+        /// </summary>
+        /// <param name="manifestParams">The details of the manifest you want to create.</param>
+        /// <returns></returns>
+        Task<Manifests.Result> CreateManifest(Manifests.Params manifestParams);
+
+        /// <summary>
+        /// Create a manifest
+        /// </summary>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call.</param>
+        /// <param name="manifestParams">The details of the manifest you want to create.</param>
+        /// <returns></returns>
+        Task<Manifests.Result> CreateManifest(Config methodConfig, Manifests.Params manifestParams);
+
+        /// <summary>
+        /// Void a label by ID to get a refund.
+        /// </summary>
+        /// <param name="labelId">The id of the label to void</param>
+        /// <returns>Result object indicating the success of the void label attempt</returns>
+        Task<VoidLabelWithLabelId.Result> VoidLabelWithLabelId(string labelId);
+
+        /// <summary>
+        /// Void a label by ID to get a refund.
+        /// </summary>
+        /// <param name="labelId">The id of the label to void</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>Result object indicating the success of the void label attempt</returns>
+        Task<VoidLabelWithLabelId.Result> VoidLabelWithLabelId(string labelId, Config methodConfig);
+
+        /// <summary>
+        /// Track a shipment using the label id
+        /// </summary>
+        /// <param name="labelId">The label id associated with the shipment</param>
+        /// <returns>An object that contains the label id tracking information</returns>
+        Task<TrackUsingLabelId.Result> TrackUsingLabelId(string labelId);
+
+        /// <summary>
+        /// Track a shipment using the label id
+        /// </summary>
+        /// <param name="labelId">The label id associated with the shipment</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>An object that contains the label id tracking information</returns>
+        Task<TrackUsingLabelId.Result> TrackUsingLabelId(string labelId, Config methodConfig);
+
+        /// <summary>
+        /// Tracks a package based on the trackingNumber and carrierCode.
+        /// </summary>
+        /// <param name="trackingNumber">The tracking number of the package you wish to track.</param>
+        /// <param name="carrierCode">The carrierCode for the trackingNumber you are using to track the package.</param>
+        /// <returns></returns>
+        Task<TrackUsingCarrierCodeAndTrackingNumber.Result> TrackUsingCarrierCodeAndTrackingNumber(string trackingNumber, string carrierCode);
+
+        /// <summary>
+        /// Tracks a package based on the trackingNumber and carrierCode.
+        /// </summary>
+        /// <param name="trackingNumber">The tracking number of the package you wish to track.</param>
+        /// <param name="carrierCode">The carrierCode for the trackingNumber you are using to track the package.</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns></returns>
+        Task<TrackUsingCarrierCodeAndTrackingNumber.Result> TrackUsingCarrierCodeAndTrackingNumber(string trackingNumber, string carrierCode, Config methodConfig);
+
+        /// <summary>
+        /// Create a label from shipment details
+        /// </summary>
+        /// <param name="labelParams">Details of the label that you want to create</param>
+        /// <returns>Object containing the created label information</returns>
+        Task<CreateLabelFromShipmentDetails.Result> CreateLabelFromShipmentDetails(CreateLabelFromShipmentDetails.Params labelParams);
+
+        /// <summary>
+        /// Create a label from shipment details
+        /// </summary>
+        /// <param name="labelParams">Details of the label that you want to create</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>Object containing the created label information</returns>
+        Task<CreateLabelFromShipmentDetails.Result> CreateLabelFromShipmentDetails(CreateLabelFromShipmentDetails.Params labelParams, Config methodConfig);
+
+        /// <summary>
+        /// Create a label from a rate id
+        /// </summary>
+        /// <param name="createLabelFromRateParams">The details of the rate that you want to use to purchase a label</param>
+        /// <returns>Object containing the created label information</returns>
+        Task<CreateLabelFromRate.Result> CreateLabelFromRate(CreateLabelFromRate.Params createLabelFromRateParams);
+
+        /// <summary>
+        /// Create a label from a rate id
+        /// </summary>
+        /// <param name="createLabelFromRateParams">The details of the rate that you want to use to purchase a label</param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>Object containing the created label information</returns>
+        Task<CreateLabelFromRate.Result> CreateLabelFromRate(CreateLabelFromRate.Params createLabelFromRateParams, Config methodConfig);
+
+        /// <summary>
+        /// Retrieve rates for a package with the provided shipment details.
+        /// </summary>
+        /// <param name="rateParams"></param>
+        /// <returns>The rates result</returns>
+        Task<GetRatesWithShipmentDetails.Result> GetRatesWithShipmentDetails(GetRatesWithShipmentDetails.Params rateParams);
+
+        /// <summary>
+        /// Retrieve rates for a package with the provided shipment details.
+        /// </summary>
+        /// <param name="rateParams"></param>
+        /// <param name="methodConfig">Configuration object that overrides the global config for this method call</param>
+        /// <returns>The rates result</returns>
+        Task<GetRatesWithShipmentDetails.Result> GetRatesWithShipmentDetails(GetRatesWithShipmentDetails.Params rateParams, Config methodConfig);
+    }
 }
\ No newline at end of file
diff --git a/ShipEngine/ShipEngineClient.cs b/ShipEngine/ShipEngineClient.cs
index 8c094dbb..980b38be 100644
--- a/ShipEngine/ShipEngineClient.cs
+++ b/ShipEngine/ShipEngineClient.cs
@@ -6,11 +6,11 @@
 using System.Net.Http.Headers;
 using System.Text.Json;
 using System.Text.Json.Serialization;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace ShipEngineSDK
 {
-
     /// <summary>
     /// ShipEngine Client is used for handling generic calls and settings that
     /// are needed for all ShipEngine API calls.
@@ -32,9 +32,19 @@ public class ShipEngineClient
 
         private const string JsonMediaType = "application/json";
 
+        /// <summary>
+        /// Modifies the client request before it is sent
+        /// </summary>
+        public Action<HttpRequestMessage>? ModifyRequest { get; set; }
+
+        /// <summary>
+        /// Token to cancel the request
+        /// </summary>
+        public CancellationToken CancellationToken { get; set; }
+
         /// <summary>
         /// Sets the HttpClient User agent, the json media type, and the API key to be used
-        /// for all ShipEngine API calls unless overrwritten at the method level.
+        /// for all ShipEngine API calls unless overwritten at the method level.
         /// </summary>
         /// <param name="config">Config object used to configure the HttpClient</param>
         /// <param name="client">The HttpClient to be configured</param>
@@ -63,6 +73,15 @@ public static HttpClient ConfigureHttpClient(Config config, HttpClient client)
             return client;
         }
 
+        /// <summary>
+        /// Sets the HttpClient User agent, the json media type, and the API key to be used
+        /// for all ShipEngine API calls unless overwritten at the method level.
+        /// </summary>
+        /// <param name="client"></param>
+        /// <param name="apiKey"></param>
+        /// <param name="baseUri"></param>
+        /// <param name="timeout"></param>
+        /// <returns></returns>
         public static HttpClient ConfigureHttpClient(HttpClient client, string apiKey, Uri? baseUri, TimeSpan? timeout = null)
         {
             client.DefaultRequestHeaders.Accept.Clear();
@@ -111,6 +130,7 @@ private async Task<T> DeserializedResultOrThrow<T>(HttpResponseMessage response)
                         error.ErrorSource,
                         error.ErrorType,
                         error.ErrorCode,
+                        response,
                         deserializedError.RequestId
                     );
                 }
@@ -143,14 +163,15 @@ public virtual async Task<T> SendHttpRequestAsync<T>(HttpMethod method, string p
         {
             int retry = 0;
 
-            HttpResponseMessage response = null;
+            HttpResponseMessage? response = null;
             ShipEngineException requestException;
             while (true)
             {
                 try
                 {
                     var request = BuildRequest(method, path, jsonContent);
-                    var streamTask = client.SendAsync(request);
+                    ModifyRequest?.Invoke(request);
+                    var streamTask = client.SendAsync(request, CancellationToken);
                     response = await streamTask;
 
                     var deserializedResult = await DeserializedResultOrThrow<T>(response);
@@ -192,13 +213,13 @@ public virtual async Task<T> SendHttpRequestAsync<T>(HttpMethod method, string p
             }
         }
 
-        private async Task WaitAndRetry(HttpResponseMessage response, Config config, ShipEngineException ex)
+        private async Task WaitAndRetry(HttpResponseMessage? response, Config config, ShipEngineException ex)
         {
             int? retryAfter;
 
             try
             {
-                retryAfter = Int32.Parse(response?.Headers.GetValues("RetryAfter").First());
+                retryAfter = Int32.Parse(response?.Headers.GetValues("RetryAfter").First() ?? string.Empty);
             }
             catch
             {
@@ -212,14 +233,15 @@ private async Task WaitAndRetry(HttpResponseMessage response, Config config, Shi
                     ErrorSource.Shipengine,
                     ErrorType.System,
                     ErrorCode.Timeout,
+                    response,
                     ex.RequestId
                 );
             }
 
-            await Task.Delay((int)retryAfter * 1000).ConfigureAwait(false);
+            await Task.Delay((int)retryAfter * 1000, CancellationToken).ConfigureAwait(false);
         }
 
-        private HttpRequestMessage BuildRequest(HttpMethod method, string path, string? jsonContent)
+        private static HttpRequestMessage BuildRequest(HttpMethod method, string path, string? jsonContent)
         {
             var request = new HttpRequestMessage(method, path);
 
@@ -231,7 +253,7 @@ private HttpRequestMessage BuildRequest(HttpMethod method, string path, string?
             return request;
         }
 
-        private bool ShouldRetry(
+        private static bool ShouldRetry(
             int numRetries,
             HttpStatusCode? statusCode,
             HttpHeaders? headers,