diff --git a/CHANGELOG.md b/CHANGELOG.md
index 06da88b..8af78df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+# v0.1.1
+
+Fix payment related bugs.
+
 # v0.1.0
 
 First draft of the SDK.
diff --git a/README.md b/README.md
index 74a20ab..f98c7b7 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# Lightspark Go SDK - v0.1.0
+# Lightspark Go SDK - v0.1.1
 
 The Lightspark Go SDK provides a convenient way to interact with the Lightspark services from applications written in the Go.
 
diff --git a/requester/requester.go b/requester/requester.go
index 935eb27..fe10a48 100644
--- a/requester/requester.go
+++ b/requester/requester.go
@@ -39,12 +39,13 @@ func (r *Requester) ExecuteGraphql(query string, variables map[string]interface{
 
 	var nonce uint32
 	if signingKey != nil {
+		rand.Seed(time.Now().UnixNano())
 		nonce = rand.Uint32()
 	}
 
 	var expiresAt string
 	if signingKey != nil {
-		expiresAt = time.Now().UTC().Add(time.Hour).Format("UnixDate")
+		expiresAt = time.Now().UTC().Add(time.Hour).Format(time.RFC3339)
 	}
 
 	payload := map[string]interface{}{
diff --git a/services/lightspark_client.go b/services/lightspark_client.go
index 20b6af0..22aa00e 100644
--- a/services/lightspark_client.go
+++ b/services/lightspark_client.go
@@ -220,7 +220,10 @@ func (client *LightsparkClient) PayInvoice(nodeId string, encodedInvoice string,
 		"encoded_invoice":    encodedInvoice,
 		"timeout_secs":       timeoutSecs,
 		"maximum_fees_msats": maximumFeesMsats,
-		"amount_msats":       amountMsats,
+	}
+
+	if amountMsats != nil {
+		variables["amount_msats"] = amountMsats
 	}
 
 	signingKey, err := client.getNodeSigningKey(nodeId)
diff --git a/version.go b/version.go
index 74014c9..168601d 100644
--- a/version.go
+++ b/version.go
@@ -1,3 +1,3 @@
 package lightspark
 
-const VERSION = "1.0.0"
\ No newline at end of file
+const VERSION = "0.1.1"