Thanks - quick reply to explain two three points. I'll look at the rest in more detail a little later

1. Your class is doing checkout handling and trolley handling (Single responsibility pattern / Cohesion). Consider having a separate Trolley object for trolley handling.

I did think of this. However, the Trolley only exists as a repository of the 'stuff' that is needed by the Stripe checkout. It isn't (intended to be) useful by itself.

3. Consider using Moo or something similar to make the OOP more ergonomic.

I expect much of the use of this module to be for small businesses using shared hosting. For this reason, I want to keep the dependencies as only core modules.

4. Exceptions are usually preferable to silent returns because they are harder to ignore (see Try::Tiny)

As above, Try::Tiny isn't core. Also, having $stripe->success is consistent with the Javascript methods provided by Stripe in stripe.js

I'm not suggesting I made the optimal choices for these, just explaining why I chose to do things the way I did.