Hey @proj_l
It seems that the part failing is the exchange of a code for a the authentication results (access_token and others). When you exchange the code for a token you need to provide the client authentication data (client_id and client_secret), the code you received, the grant type (authorization_code) and the redirect_uri you originally provided (see Add Login Using the Authorization Code Flow for more information on what goes on under the hood).
Are you using our quickstart (Auth0 Python SDK Quickstarts: Login) as guidance? If so, the SDK should take care of providing the expected parameters when doing the code exchange (Auth0 Python SDK Quickstarts: Login).
If not, follow your code to make sure that the redirect_uri originally provided in the /authorize request is also included in the /oauth/token request from the callback handler.