I'm glad I could clarify how it works.
I couldn´t find any way to change this mail. Is it possible to set up this email
Sure, you'll find the setting here: WP Admin > s2Member > PayPal Options > Specific Page/Post Confirmation Email (or Stripe Options if you're using that gateway)
I´m still wondering, what will happen, if this same user wants to buy a second gift certification. Or a third one.
Ah, I see what you mean... If he goes back to that page where the gift certs generator is, it'll show the original created for him and its used status.
As long as the shortcode, the page ID, and the user are the same, the generated code will be the same, but if you change one of those three, new codes are generated.
So if you change the generator to create more codes now, even the first one will change...
I can see how this can be improved. I'm making a note for as a feature request for future improvement.
In the meantime, yeah, if you want to sell several coupon codes to the same user, you would either have separate pages (or use conditionals on the same page) and sell separate ccaps for each, or you can use the Specific Post/Page Restriction.
If I had to do this for myself in your situation, I'd probably go with the Specific Post/Page Restriction, set the time to only 1 hour (use the
exp attribute in the pro-form shortcode). That would be enough for him to go get the code right away, but maybe he won't be quick enough to think about abusing the system. WP Admin > s2Member > PayPal Pro-forms > Shortcode Attributes Explained > exp
You can also make the Unique IP restriction a bit tighter. WP Admin > s2Member > Restriction Options > Unique IP
Does that help?