Bespoke download system for digital goods, using paypal

I’m using firebase for account management for a digital goods shop. That works fine with the standard stripe credit card checkout form, but I’m running into a potential issue when I try to use paypal. The email address used for paypal might not match the one they are using for their account on my site. If that happens, the product ownership will be assigned to the wrong account and the user won’t see it appear on the site.

Is there a way for me to change the email value in the paypal checkout request? I tried swapping out the display text, but understandably that doesn’t work.

Alternatively, I could send the user’s email as metadata, but I don’t know how I can add to the form so that it will post with the webhook payload.

Here is my site Read-Only: LINK