Sebagai catatan pribadi, sebelum setting backup, rubah dulu konfigurasi tweak setting :
Internal case CPANEL-15021 where attempting to generate credentials when setting up a Google Drive backup destination results in a "HTTP Error 401: You do not have permission to access this page" error message. I'll monitor this case and update this thread with more information as it becomes available. In the meantime, a workaround is to temporarily disable "Referrer safety check" under "Security" in "WHM >> Tweak Settings" when generating the credentials, and then enable it again after the backup destination is configured.
Update: This case is scheduled for inclusion with cPanel version 68.