The Partners API uses standard HTTP response codes to show if an API request was successful or unsuccessful. All in all: Success is indicated by codes in the range 2xx. Codes in the 4xx range signify errors that couldn't be fixed based on the information available (e.g., a necessary parameter was left out, etc.). A server error (rare) is indicated by codes in the 5xx range.

Have a look at the error below you are encountering to go straight to the causes as well as solutions

400Bad Request
401Invalid Key