External courses that can be used within the academy via coupons have a max quota and an expiration date. The coupon quota are being decreased every time a user gets enrolled in the relevant course. Unassigning a user from a coupon course will not increase the remaining coupon quota.
Please note: Coupons are not interchangeable and there is no way to remove a coupon from a user. Coupons are automatically revoked only in cases where a user that is enrolled in the course and has no completion in it, gets deactivated. Read also: Revoked Coupons Functionality
Coupon courses can be located under the Training Admin Workspace, under External Courses -> Coupons.