You can connect Stripe, PayPal or any other payment gateway that has an option to redirect clients to another URL with a specific program.
Simply add an invite link as a redirect page after the checkout and your clients will land in the program. Here's how our co-founder David did it for his program > https://www.loom.com/share/fce19768d798492aa3bf1fe93a676604
If you have more questions about this, you can choose to:
Start a chat in the lower right corner.