The app isn’t PureGyms core business though. I’d rather they spend £200k on extra squat racks in the gyms than on better UX on their app.

I can just memorise the 8 digit entry code and never ever open the app.

In a single weekend the OP changed the app experience from “somewhat annoying and frustrating” to “very convenient”.

The budget required to improve the customer experience is near nothing, but I suspect no one at PureGym has actually evaluated that the experience is really not great, they probably don’t have the experience or expertise to do so.