Ultimate Affiliate Pro - How to change a link based on the referring affiliate?

This may be simple, but I’ve been going in circles. I’d love some help if you don’t mind taking a quick look.

I am new to UAP but I’ve seen this done quite nicely, but in reverse.

The model is this:
People buy an MRR product from me, and I want to help them sell it by providing a multi-page sales funnel with a button on the checkout page that changes based on what they entered in a custom field in their affiliate portal.

Opt-in page: (hosted elsewhere, but redirects to their aff link on my site)
Thank You Page: They watch a welcome video and click a link to a replay page.
Video page: This page shows a video and has a button that sends them to a checkout page.

Checkout page: This page has a button with a URL that needs to change based on a personal payment link that the affiliate has entered in their affiliate portal.

The benefit to them is they don’t get bogged down by the techie stuff that normally kills progress, and can immediately start promoting their new cloned site.

The benefit to me is that I can sell them services on the backend.

This model probably sounds familiar, but the thing that I’m not “getting” is how to embed the individual’s payment link (Square/Stripe, etc.) into the checkout button.

Am I just missing something simple?

Thank you. I have done that several times and by the ticket system, chat and including a Loom video as well. I’m hoping to hear back from them before the refund window expires.

I really want to use this software. It looks great.
I have been searching YT, their help section for case-studies and walkthroughs, as well as ChatGPT but coming up wanting.