Ok I eventually managed.

The solution is using the "discount for next order" type of voucher.

You create a voucher tag, a voucher product (published), and a voucher sale product (not published).

Also you have to create an "email" delivery method, and set it so that it's only available for products tagged voucher.

And for your normal delivery methods you have to exclude products tagged voucher.

This is the configuration:

And this is the final product if you're curious: https://shop.otterspace.ie/shop/otter-voucher-10eur-1518

Hi,

Please refer to the Module:

1. https://www.odoo-community.org/shop/website-sale-loyalty-page-715486

2. https://apps.odoo.com/apps/modules/12.0/website_coupon

Hope it helps