diff --git a/src/main/java/site/billbill/apiserver/api/chat/dto/response/ChatResponse.java b/src/main/java/site/billbill/apiserver/api/chat/dto/response/ChatResponse.java
index 05f2619..b0290a0 100644
--- a/src/main/java/site/billbill/apiserver/api/chat/dto/response/ChatResponse.java
+++ b/src/main/java/site/billbill/apiserver/api/chat/dto/response/ChatResponse.java
@@ -3,7 +3,6 @@
 import com.fasterxml.jackson.annotation.JsonFormat;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
-import java.util.List;
 import lombok.Builder;
 import lombok.Getter;
 
@@ -33,6 +32,7 @@ public static class ViewChatInfoResponse {
         private int unreadCount;
         private String lastChat;
         private String lastSender;
+        @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ss.SSS")
         private LocalDateTime updatedAt;
         private String opponentId;
         private String opponentNickname;
diff --git a/src/main/java/site/billbill/apiserver/api/chat/service/ChatServiceImpl.java b/src/main/java/site/billbill/apiserver/api/chat/service/ChatServiceImpl.java
index a788033..7615f59 100644
--- a/src/main/java/site/billbill/apiserver/api/chat/service/ChatServiceImpl.java
+++ b/src/main/java/site/billbill/apiserver/api/chat/service/ChatServiceImpl.java
@@ -103,6 +103,10 @@ public List<ViewChatInfoResponse> getChatList(String beforeTimestamp, String use
         }
 
         ChatInfoList webhookResult = webhookService.sendWebhookForChatList(activeChatIdsByUserId, beforeTimestamp);
+        if (webhookResult == null || webhookResult.getChatInfoList() == null || webhookResult.getChatInfoList().isEmpty()) {
+            return Collections.emptyList();
+        }
+
         List<ChatInfo> chatInfoList = webhookResult.getChatInfoList();
 
         return chatInfoList.stream().map(chatInfo -> {
diff --git a/src/main/java/site/billbill/apiserver/api/chat/service/WebhookServiceImpl.java b/src/main/java/site/billbill/apiserver/api/chat/service/WebhookServiceImpl.java
index c73f03e..3fba597 100644
--- a/src/main/java/site/billbill/apiserver/api/chat/service/WebhookServiceImpl.java
+++ b/src/main/java/site/billbill/apiserver/api/chat/service/WebhookServiceImpl.java
@@ -2,6 +2,8 @@
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -23,10 +25,11 @@ public class WebhookServiceImpl implements WebhookService {
 
     @Autowired
     public WebhookServiceImpl(@Value("${webhook.url}") String webhookUrl,
-                              WebClient.Builder webClientBuilder,
-                              ObjectMapper objectMapper) {
+                              WebClient.Builder webClientBuilder) {
         this.webClient = webClientBuilder.baseUrl(webhookUrl).build();
-        this.objectMapper = objectMapper;
+        this.objectMapper = new ObjectMapper();
+        this.objectMapper.registerModule(new JavaTimeModule()); // Java 8 시간 타입 지원
+        this.objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS); // 배열 대신 ISO-8601 사용
     }
 
     public void sendWebhookForChatRoomCreate(String channelId, String contact, String owner) {
@@ -49,6 +52,9 @@ public void sendWebhookForChatRoomCreate(String channelId, String contact, Strin
     }
 
     public WebhookRequest.ChatInfoList sendWebhookForChatList(List<String> chatRoomIds, String beforeTimestamp) {
+        if (beforeTimestamp == null) {
+            beforeTimestamp = "";
+        }
         String jsonResponse = webClient.post()
                 .uri("/chat/list")
                 .bodyValue(Map.of(
@@ -58,10 +64,13 @@ public WebhookRequest.ChatInfoList sendWebhookForChatList(List<String> chatRoomI
                 .retrieve()
                 .bodyToMono(String.class)
                 .block();
+        log.info(jsonResponse.toString());
         try {
-            return objectMapper.readValue(jsonResponse, WebhookRequest.ChatInfoList.class);
+            WebhookRequest.ChatInfoList result = objectMapper.readValue(jsonResponse, WebhookRequest.ChatInfoList.class);
+            return result;
         } catch (JsonProcessingException e) {
-            throw new RuntimeException(e);
+            throw new RuntimeException("JSON Parsing Error", e);
         }
+
     }
 }