In version 3.3.4 when a 100% off coupon is applied the stripepayment_free_enrolsettings function in externallib.php is called. But this function is missing the code to create the customer in Stripe or update the customer with the coupon. As a result the coupon is not redeemed. If you have a coupon with the limited number of redemptions then this is a problem.
In version 3.3.4 when a 100% off coupon is applied the stripepayment_free_enrolsettings function in externallib.php is called. But this function is missing the code to create the customer in Stripe or update the customer with the coupon. As a result the coupon is not redeemed. If you have a coupon with the limited number of redemptions then this is a problem.
I have a patch for this issue: stripepayment-free-enrol.patch