diff --git a/linebot/messaging_api/model_narrowcast_progress_response.go b/linebot/messaging_api/model_narrowcast_progress_response.go
index d2a93f60..6d45cb7b 100644
--- a/linebot/messaging_api/model_narrowcast_progress_response.go
+++ b/linebot/messaging_api/model_narrowcast_progress_response.go
@@ -54,7 +54,7 @@ type NarrowcastProgressResponse struct {
 	FailedDescription string `json:"failedDescription,omitempty"`
 
 	/**
-	 * Error summary. This is only included with a phase property value of failed. One of:  `1`: An internal error occurred. `2`: An error occurred because there weren't enough recipients. `3`: A conflict error of requests occurs because a request that has already been accepted is retried.
+	 * Error summary. This is only included with a phase property value of failed. One of:  `1`: An internal error occurred. `2`: An error occurred because there weren't enough recipients. `3`: A conflict error of requests occurs because a request that has already been accepted is retried. `4`: An audience of less than 50 recipients is included as a condition of sending.
 	 */
 	ErrorCode int64 `json:"errorCode"`