That’s a good question.
Once you have linked the icon from your edited design with the URL of the page with your amazon gift card, there’s no need to add any email address to your design.
If you have an Amazon account, that requires your email address.
The gift card added to your Amazon is enough.
No need to add an email address, but you you want to make your email address public, simply type it as simple plain text on your custom bio design something like:
” Send your Amazon gift card to my-email@address.com “