How to create a Name The Price product

[hopinn]

How can i create a product in Virtuemart for which a website visitor can enter an amount for the product himself, e.g. for a gift voucher to eat in a physical restaurant? Can you then immediately include a qr code in the purchase email to verify this gift voucher when scanned by the restaurant owner? With a custom field setting? Or with a plugin? Which one? Thank you.