API returning 403 Forbidden errors

Hello. The API started returning 403 Forbidden errors a couple weeks ago (only in sandbox mode, production seems to work just fine).

The sandbox api key is correct and it is properly added to the headers (so basically nothing changed).

What are the possible causes of 403 errors?

Any help would be appreciated.

Hi! Can you give me the hostname for your sandbox account? Which API endpoint are you try to call?