First I make a request to /oauth2/authorize which includes response_type, client_id, response_uri, state, scope. This will redirect me to medplum app from redirect uri and prompt me to login. After logging in, it will provide me with a code. I can then use this code for /oauth2/token in which I pass a new header Authorization: Basic and then it will return 200 OK. Now, do I pass this header when accessing /fhir/R4, which will also give the same error.