Due to the new restrictions being imposed by Google on accessing files from Google Drive, the app now defaults to limited access on Google Drive. This means that it can only access files that were created by the app itself. Since the free and the Pro version of the app are 2 separate apps, this also means that the Pro version cannot access files created by the free version and vice-versa.
Another issue with this access restrictions is that the app also cannot see any folders that were created directly in Google Drive for storing backups in specific folders.
In most cases, this is usually not a problem as you just keep using the app (free or Pro) that you used to create the backup and it can always access the files that it created. It becomes a bit more problematic if you move from the free to the Pro version as the Pro version cannot access the files created by the free version.
To view or restore backups that are not directly visible in the app, you can use the Google Drive app to access the backup files. Once you have the file select or open, use the 3 dots menu and select “Open With”. On the next screen, select the SMS Backup & Restore app that you have installed.