Everyone building a web2app funnel (quiz → paywall → web checkout → open the app) talks about conversion rate on the quiz and paywall. Almost nobody talks about the step right after checkout, where the app has to recognize a user who just paid on a completely different surface - and that's the step that actually determines whether the funnel was worth building.

Why this is the hard part

The web checkout and the native app are, from an engineering standpoint, two different clients with two different identity contexts. The web session knows an email, a payment method, and whatever the quiz collected. The app, on first open, knows nothing. Bridging that gap with a deep link or a login screen sounds trivial until you actually have to handle:

The app isn't installed yet.…