Customer email confirmation

Hello and thanks for that awesome plugin.

In general the plug-in seems to work fine. But actually I do not know how to force the customer to give an email address, so that I can send the download-link also via email. (I offer an ebook and I want the customer to get the download-link also via mail, so that I can avoid reclamations, when the may lose the file).

Thanks!

https://wordpress.org/plugins/gourl-bitcoin-payment-gateway-paid-downloads-membership/