If its a website where you design and make it, you should be able to add a link to a page. Its that simple and just provide some information about how it works.
I need to amend mine and it certainly isnt the best by any means.
On face book, just type in the link and give a description. Or if the customer uses a smart phone, which most do (or a tablet via email). Send them the link via text and so when they receive the text, they can click on it there, as you can on my previous post and it will take them there.
https://www.1nkservices.co.uk/payments