Confirm: The money is there
The customer gets their 4-digit pickup code straight away.
Payment short: Some of it arrived
Type the amount you received. The bot asks the customer for the exact remainder on the same order, and they send a second screenshot for you to check.
Fake: Nothing arrived
The order is cancelled and the customer is told.
A screenshot is not proof of payment; your bank account is. Check it before you tap Confirm. If the rest of a short payment doesn't arrive in time (60 minutes by default), the order is cancelled and the bot tells you both how much is owed back.