Explanation

Correct choice is: "The external API reported an error with the HTTP request that was received from the outbound HTTP Request operation of the Mule application"

Understanding HTTP 4XX Client Error Response Codes : A 4XX Error is an error that arises in cases where there is a problem with the user’s request, and not with the server.

Such cases usually arise when a user’s access to a webpage is restricted, the user misspells the URL, or when a webpage is nonexistent or removed from the public’s view.

In short, it is an error that occurs because of a mismatch between what a user is trying to access, and its availability to the user — either because the user does not have the right to access it, or because what the user is trying to access simply does not exist. Some of the examples of 4XX errors are

400 Bad Request The server could not understand the request due to invalid syntax. 401 Unauthorized Although the HTTP standard specifies "unauthorized", semantically this response means "unauthenticated". That is, the client must authenticate itself to get the requested response. 403 Forbidden The client does not have access rights to the content; that is, it is unauthorized, so the server is refusing to give the requested resource. Unlike 401, the client's identity is known to the server. 404 Not Found The server can not find the requested resource. In the browser, this means the URL is not recognized. In an API, this can also mean that the endpoint is valid but the resource itself does not exist. Servers may also send this response instead of 403 to hide the existence of a resource from an unauthorized client. This response code is probably the most famous one due to its frequent occurrence on the web. 405 Method Not Allowed The request method is known by the server but has been disabled and cannot be used. For example, an API may forbid DELETE-ing a resource. The two mandatory methods, GET and HEAD, must never be disabled and should not return this error code. 406 Not Acceptable This response is sent when the web server, after performing server-driven content negotiation, doesn't find any content that conforms to the criteria given by the user agent. The external API reported that the API implementation has moved to a different external endpoint cannot be the correct answer as in this situation 301 Moved Permanently The URL of the requested resource has been changed permanently. The new URL is given in the response. ----------------------------------------------------------------------------------------------------------------------------------------------- In Lay man's term the scenario would be: API CLIENT —> MuleSoft API - HTTP request “Hey, API.. process this” —> External API API CLIENT <– MuleSoft API - http response "I'm sorry Client.. something is wrong with that request" <– (4XX) External API