A quick search revealed lots of interesting information.
https://docs.moodle.org/403/en/Enrolment_on_payment
Integrations exist for AuthorizeNet https://moodle.org/plugins/enrol_authorizedotnet) and Stripe (https://moodle.org/plugins/enrol_stripepayment)
Also, probably better to ask this question in the Authentication forum https://moodle.org/mod/forum/view.php?id=42 or maybe the enrollment forum.
https://docs.moodle.org/403/en/Enrolment_on_payment
Integrations exist for AuthorizeNet https://moodle.org/plugins/enrol_authorizedotnet) and Stripe (https://moodle.org/plugins/enrol_stripepayment)
Also, probably better to ask this question in the Authentication forum https://moodle.org/mod/forum/view.php?id=42 or maybe the enrollment forum.
Moderator note: No need to re-post your question Symon, as I'm moving this discussion to the Enrolment forum as suggested by Eric...