Good write-up here.
Enable ADB verbose logging for backups:
adb shell setprop log.tag.GmsBackupTransport VERBOSE
adb shell setprop log.tag.BackupXmlParserLogging VERBOSE
Force auto backup:
adb shell bmgr backupnow <PACKAGE>
Force full backup:
adb shell bmgr fullbackup <PACKAGE>
Force all pending backup operations to run immediately by using the bmgr run command:
adb shell bmgr run
At this point you can uninstall and reinstall the app to be prompted to restore when opening it again.
Get the backup token:
adb shell dumpsys backup | grep Current
Force restore:
adb shell bmgr restore <TOKEN> <PACKAGE>
If you want to wipe the backup and can't do it because the it is unclear how to call the wipe properly you could try to disable and enable the auto backup.
adb shell bmgr enable false
adb shell bmgr enable true
Please let us know what is TOKEN & PACKAGE