This is my first time using PlayFab with Unity. I have been trying to resolve the issue described below for over 2 weeks now to no avail.
The problem is regarding PlayFab's LoginUsingGoogle(). The function requires an oAuth code. Fetching the code, however, is not being done using Google's libraries (as described in PlayFab's documentation). I am using a Unity plugin called Cross-Platform Native Plugins. The plugin provides functionality to communicate with both Google and iOS cloud features (including logging in). I, therefore, am getting the oAuth code using CPNPs LoadExternalAuthenticationCredentials().
CPNP's Google Play login works just fine, but when trying to call PlayFab's API to link/login the Google account using the fetched oAuth code the error in the title appears.
I have been through every resource related to the issue on PlayFab's website and have been discussing the issue with CPNP's support for days with no result as the problem appears to be a PlayFab one.