That is FRP (Factory Reset Protection) . Google requires the previous owner’s Gmail/Password. Sunmi devices are notoriously difficult to bypass FRP on without flashing new firmware via a PC (using SP Flash Tool). Your best bet is to contact the previous admin or Sunmi support.

Before you hard reset, take a photo of your POS app’s serial number or license key. You will need it to reactivate.

Have you ever been locked out of a Sunmi terminal? Let me know in the comments how you solved it.

: Once finished, select Reboot system now to restart the device. Standard Factory Reset (Settings Menu)