What does http 403 mean as response?

[cklm]

When fetching deals, we see http 403 (forbidden) as response the last days. We already know about http 401 (unauthorized), which means, that the api-credentials are wrong. What does 403 mean in that case? What does the user have to change, when this error happens?

[Chris-Kaye]

HTTP Error 403 means "malformed request".

If you can post the request here (removing your signature) we might be able to help.
If could simply be a problem with the query string or request body you are sending, like a typo in your code.