Go to Settings → Account and sign in with your Google account.
Check your available Drive storage at drive.google.com. Free Google accounts have 15 GB. Rasmerk backups are small (usually under 10 MB), but if your Drive is full, backups fail.
Google Drive backup requires an active internet connection. Connect to Wi-Fi or mobile data and try again.
Google Drive backup requires Premium. Verify your Premium status in Settings → Premium.
On some Android versions, Rasmerk needs permission to access Google Drive. Re-sign in from Settings → Account.
Go to Settings → Backup → Google Drive → Back Up Now.