When your computer says no, it's helpful to know how to make it say yes. Below is a summary of error codes and corresponding HTTP status codes for the OAuth 2.0 flow.

Error Code Description
invalid_request 400 The request is malformed, a parameter has an invalid value or is missing.
invalid_client 401 Client authentication failed.
unauthorized_client 400 Client is not authorized to use the grant.
unsupported_grant_type 400 Authorization grant is not supported by the Authorization Server.
invalid_scope 400 The scope is malformed or invalid.