Okay, as far as I can see, everything is working correctly.
There may be a little misunderstanding in terms of what happens after the payment. This is what will happen:
After the payment, the customer will be sent to a “Thank You” page (it can be any page on your site). On this page you should tell them to check the email and click on the special link that was sent to them.
Nothing will happen until the customer clicks on that special link sent to their email. Can you click on that link that you receive in the email after purchase and complete the registration? If you cannot do the registration by clicking on the link, please share the that special link URL here so I can check it.