Indicate at the checkout that you want to make an OXXOPay payment
Tell the cashier the reference number on this tab so that they can type directly on the sales screen.
Make the corresponding payment with cash.
When confirming your payment, the cashier will give you a printed receipt. You can verify that the payment has been made correctly. Keep this proof of payment.
Once you have completed these steps you will receive an email from First Aid confirming your payment.