Final answer:
The correct function key to use for debit or credit card transactions depends on the specific programming of the point-of-sale terminal, which is not provided in the question. It's imperative to consult the POS system's manual to determine the correct key.
Step-by-step explanation:
The question specifically asks about the functions of keys on a payment system, likely referring to a point-of-sale (POS) terminal. As a tutor, it's important to clarify that without context or a manual for the specific payment system, we cannot definitively say what each function key (F1, F2, F3, F4) does. Most modern POS systems are designed to accept payments via debit cards and credit cards. When a customer plans to pay with either of these cards, you would typically use the key associated with card payments, as described in the user manual for the payment system being used. Remember that a debit card is directly tied to a customer's bank account, allowing them to access their funds, and it can often act similarly to a credit card during transactions.
- Function Key (Whichever is programmed for card payments)