Comic Store Subscription Service for WP site

[JordanGum]

I'm building out a comic book store client's site and trying to set up a subscription service component similar to this one. It uses Manage Comics, a Shopify-based third-party app/service, which imports monthly inventory from all of the individual publishers.

The barrier that I've run into is that they are using the Square POS system in the physical store, currently, but I haven't been able to find a comparable Square-based solution yet. If anyone on here has a suggestion, I and my client would greatly appreciate the help. Thanks!