Usually this is due to a time difference between your phone and the Senly server. TOTP codes are only valid for 30 seconds and use server clock time.
Fix it like this:
1. Sync the time on your phone (enable automatic network time)
2. Wait until your app shows a new code and use that immediately
3. Verify you haven't scanned an old QR code — if you reconfigured 2FA, only the newest entry works
Still not working? Use your backup code or ask a fellow admin to temporarily reset your 2FA.