Extend User Forms to Require a Paypal Payment

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Silverstripe Version: 4

Question: Extend User Forms to Require a Paypal Payment
I have installed the new user forms module which allows editing forms from within the CMS. Though, I can’t figure out how to modify how the form handles the submission. I want the form to include a Paypal payment before you can submit it.

Does anybody know how I can do this?