code: public void getToken(String authorizationCode, @NonNull final AuthCallback callback) {
          apiClient.token(authorizationCode, redirectUri)
                  .setCodeVerifier(codeVerifier)
                  .start(new BaseCallback<Credentials, AuthenticationException>() {
                      @Override
                      public void onSuccess(Credentials payload) {
                          callback.onSuccess(payload);
                      }
  
                      @Override
                      public void onFailure(AuthenticationException error) {
                          if ("Unauthorized".equals(error.getDescription())) {
                              Log.e(TAG, "Please go to 'https://manage.auth0.com/#/applications/" + apiClient.getClientId() + "/settings' and set 'Client Type' to 'Native' to enable PKCE.");
                          }
                          callback.onFailure(error);
                      }
                  });
      }
docs: Performs a request to the Auth0 API to get the OAuth Token and end the PKCE flow.
  The instance of this class must be disposed after this method is called.
  
  @param authorizationCode received in the call to /authorize with a "grant_type=code"
  @param callback          to notify the result of this call to.