There is a built-in payment form that might suit your needs, you can find more info about it here.
If you have more questions about it, you can contact Wix Support and they'll be able to help you.
If you want to create a custom registration form with payment, you can use the Wix Pay API to do it.
E.g. have a conditional statement which enters data into the database only if the payment is successful.
Corvid Tutorial: Processing Payments