The RefreshAt is a week, but if the code is actually valid for a week, it's not clear why a simple screenshot of the code didn't work.

Because you’d have to waste the time to take a new screenshot every week, of course.

It seems like it did work and they didn't want to deal with manually updating it weekly

I don't know security that well but if the puregym app refreshes the token then the old tokens would expire immediately right?

Nope. As I read it, any token less than a week old would work. So for any user, they have 7 * 24 * 60 tokens live at any time.

He said the code from Monday didn't work on Tuesday

Yeah, screenshot on Monday, messed with the app that evening, tried using it Tuesday morning -- dead.

I've seen people on PureGym's Twitter successfully refreshing screenshots weekly though, and the API response suggests the same.

That being said, I couldn't find a validation endpoint to check if mine got invalidated by something specific (maybe signing out?) or if there's some other magic happening.

I wonder if opening the app invalidated it, and those people who had it working just screenshot once.

My gym has a similar system but I realised it's time based and the app functions without Internet. I installed the app onto an old android with no sim, logged in at home over WiFi and it successfully regenerated QRs without data

no

Probably invalidates old tokens when a new one is generated.

I think ideally you'd do it maybe every day or so, so that if the user goes offline for a while, or the server you're running goes down or something, the pass will continue to work for at least 6 days. It buys you a lot of time to fix things.