Important: This website is now read only (except to admins) to comply with the UK Online Safety Act. Composr CMS is in the process of migrating to a new Constitutional governance model and Bazaar development model, with functionality of the old website (constructed by ocProducts Ltd, the prior copyright holder, a UK company) spread between GitLab and the new website (which has no connections to the UK).
There is a tracker issue for including Stripe @ 0001536: Payment gateway: Stripe - Composr CMS feature tracker which means it's a possibility if the issue gets sponsorship. Otherwise it may happen for free at some point along the way, but given it's something that only a few may want/need it's more likely to happen as a result of community members financing it.