The cash drawer opens when you click on the lock in the number keypad during the payment process

automatically after each cash payment, if the "Open cash drawer after payment" option is enabled in the "Settings" → "Printer".

every time you open or close a shift with the lock sign in "Menu" → "Cash journal", or make adjustments with the "Cash journal sign".

If the drawer still does not open, it may be that the cash register is locked with the key and thus blocked.