What are the differences between 401 Unauthorized and 403 Forbidden errors in Postman?

A 401 Unauthorized error means the client hasn't provided valid authentication credentials (like an API key). It suggests authentication is required. A 403 Forbidden error means the client *has* authenticated, but doesn't have permission to access the requested resource. Essentially, 401 is about *who* you are, while 403 is about *what* you're allowed to do.