List of Access Token Request Errors and Error Response

Response Reason
unsupported_grant_type Wrong grant_type is used in the request.
invalid_request Grant_type is missing.
invalid_client Wrong or missing client information.
invalid_grant The authorization code is invalid or expired.
server_error Unknown server error occurred.

For example, an error response can be as follows:

statusCode : 401 
statusMessage : "Unauthorized" 
content : { 
  "error_description":"Client authentication failed","error":"invalid_client" 
} 
content-type : "application/json;  
charset=utf-8"