Add Apple pay to website via a third party payment gateway

We have an operational website that currently has credit card and google pay as payment options. We would like to extend the payments to include apple pay. The apple pay is provided via a third party gateway. There is an existing process for payments that you must follow.

This project will require PHP, MYSQL and some front end html.

I require a list of all files changed at the end of the project.

Please read attached document for details on the payment gateway.