diff --git a/linebot/v3/messaging/models/narrowcast_progress_response.py b/linebot/v3/messaging/models/narrowcast_progress_response.py
index 8fb8d27f..74e8349b 100644
--- a/linebot/v3/messaging/models/narrowcast_progress_response.py
+++ b/linebot/v3/messaging/models/narrowcast_progress_response.py
@@ -31,7 +31,7 @@ class NarrowcastProgressResponse(BaseModel):
     failure_count: Optional[StrictInt] = Field(None, alias="failureCount", description="The number of users who failed to send the message.")
     target_count: Optional[StrictInt] = Field(None, alias="targetCount", description="The number of intended recipients of the message.")
     failed_description: Optional[StrictStr] = Field(None, alias="failedDescription", description="The reason the message failed to be sent. This is only included with a `phase` property value of `failed`.")
-    error_code: Optional[StrictInt] = Field(None, alias="errorCode", description="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_code: Optional[StrictInt] = Field(None, alias="errorCode", description="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. ")
     accepted_time: datetime = Field(..., alias="acceptedTime", description="Narrowcast message request accepted time in milliseconds.  Format: ISO 8601 (e.g. 2020-12-03T10:15:30.121Z) Timezone: UTC ")
     completed_time: Optional[datetime] = Field(None, alias="completedTime", description="Processing of narrowcast message request completion time in milliseconds. Returned when the phase property is succeeded or failed.  Format: ISO 8601 (e.g. 2020-12-03T10:15:30.121Z) Timezone: UTC ")