diff --git a/index.ts b/index.ts
index c045d4c..07710e3 100644
--- a/index.ts
+++ b/index.ts
@@ -143,9 +143,10 @@ export class AppStoreServerAPIClient {
         try {
             const responseBody = await response.json()
             const errorCode = responseBody['errorCode']
+            const errorMessage = responseBody['errorMessage']
 
             if (errorCode) {
-                throw new APIException(response.status, errorCode)
+                throw new APIException(response.status, errorCode, errorMessage)
             }
 
             throw new APIException(response.status)
@@ -369,11 +370,13 @@ export class AppStoreServerAPIClient {
 export class APIException extends Error {
     public httpStatusCode: number
     public apiError: number | APIError | null
+    public errorMessage: string | null
 
-    constructor(httpStatusCode: number, apiError: number | null = null) {
+    constructor(httpStatusCode: number, apiError: number | null = null, errorMessage: string | null = null) {
         super()
         this.httpStatusCode = httpStatusCode
         this.apiError = apiError
+        this.errorMessage = errorMessage
     }
 }
 
@@ -437,7 +440,7 @@ export enum APIError {
      * 
      * {@link https://developer.apple.com/documentation/appstoreserverapi/invalidrequestidentifiererror InvalidRequestIdentifierError}
      */
-    INVALID_IDENTIFIER = 4000011,
+    INVALID_REQUEST_IDENTIFIER = 4000011,
 
     /**
      * An error that indicates that the start date is earlier than the earliest allowed date.
diff --git a/tests/unit-tests/api_client.test.ts b/tests/unit-tests/api_client.test.ts
index 17cb9e0..16566ad 100644
--- a/tests/unit-tests/api_client.test.ts
+++ b/tests/unit-tests/api_client.test.ts
@@ -417,6 +417,7 @@ describe('The api client ', () => {
             let error = e as APIException
             expect(error.httpStatusCode).toBe(500)
             expect(error.apiError).toBe(APIError.GENERAL_INTERNAL)
+            expect(error.errorMessage).toBe("An unknown error occurred.")
          }
      })
 
@@ -435,6 +436,7 @@ describe('The api client ', () => {
             let error = e as APIException
             expect(error.httpStatusCode).toBe(429)
             expect(error.apiError).toBe(APIError.RATE_LIMIT_EXCEEDED)
+            expect(error.errorMessage).toBe("Rate limit exceeded.")
          }
      })
 
@@ -453,6 +455,7 @@ describe('The api client ', () => {
             let error = e as APIException
             expect(error.httpStatusCode).toBe(400)
             expect(error.apiError).toBe(9990000)
+            expect(error.errorMessage).toBe("Testing error.")
          }
      })