Force email value after Paypal authorization

I’m using firebase to manage login on the site. I product ownership (digital stuff) by adding claims to the user objects when the webflow purchase hook hits my server.

I’d like to add paypal as a payment gateway, but it seems like the current integration forces me to use the paypal-associated email. The problem is that I can’t assign ownership unless I know the user’s email address. e.g. I can log in to the site using me@hotmail.com, but use my paypal account on me@gmail.com.

Is there a clean solution to this? How can I send the user’s email along with the paypal purchase?