Yes, it becomes an in service credit system, which is pretty clear to the user and most of us experencied that at some point.

It becomes messy when you have more credits than you could ever consume, as the service will be reluctant to emit refunds (making them harder to get also pushes the user to consume them instead...yes, dark patterns...), but I think it's a good system.

I personnaly think it works better when it's not auto renewed (so not a subscription), as it engages the user in the ownership of the credit and naturally reduces the refund part. Getting new credits can still be as simple as pressing a button, so friction can be reduced.