How to cancel an incorrect Apple Pay Payment

Of course Apple Pay is a thing, the point was that the answers to the topic in your original post referred to iMessage and that is only for sending money using Apple Cash. That is why the payment shows in iMessage, because that is where you send and receive Apple Cash.

You did not send money with Apple Cash so those instructions do not apply to your situation at all. You will need to contact the merchant to cancel the transaction or request a refund. Any refund will go directly to the card that was used with Apple Pay. Refunds do not go to Apple Pay because it is not a bank. Apple Pay only allows your bank to provide the merchant your account details securely, so you are not typing in your account number on a website.

Do you mean Apple Cash? Apple Cash payments that have not yet been accepted can be canceled in iMessage by long-pressing on the amount and selecting from the menu. There is no such thing as an Apple Pay payment; Apple Pay is a conduit between your card issuer and merchant. If you have issues, contact either.

Yes, Apple Pay is a conduit that provides secure payment between the merchant and the card issuer. It is not a bank, card issuer, or account on which you have funds. If you believe you have been charged incorrectly, contact the merchant. Something else? Contact the card issuer of the card that you used.