I'd like to setup a discount for new subscribers to a newsletter, in Odoo 19 Enterprise saas.
I tried with automated server actions, and promotions, and pricelists, but can't reach the scope.

Requests:

• when a website visitor subscribes to a newsletter, receive a welcome e-mail and a 10% discount
• the subscriber can use the discount one time only
• the discount works only if the customer is in the newsletter

the challenge is to validate the discount to the right customer, because the model "contact for e-mail marketing" is different to the model "partner" (I don't remember the right names in English)