Regarding the FairPlay voucher, another client customized their registration form as follows:
(Schreenshot #1 - Online Registration Form)
(Schreenshot #2 - Invoice)
If people want to use the FairPlay voucher, they have to enter the voucher number. If not, they can't submit the form.
This means they must first get their voucher number before they fill out the registration form.
Let us know If you also want to apply this customisation to your online registration form.