Newbie to Expo, stuck adding Auth0 to app running on physical iPhone

We’re building our app using Expo and React Native. We use Auth0 for user authentication.

On the Android emulator, the app runs perfectly. On the iPhone simulator, the app runs mostly perfectly. The only unexpected behavior is that just before the app launches the in-app web browser for log in or log out, it pops up a permissions window:


According to the Auth0 person’s response in this conversation from 2019 ("APP" Wants to Use "" to Sign in), that permissions pop-up only happens when the app is running on localhost. That makes sense — my web apps do something similar when I run them on localhost.

So I created an Expo “preview” build to run the app on my physical iPhone. But darn! On my physical device, where it should be executing authentication code, it displays a blank screen.

Has anyone encountered this? How did you fix it?

Using Expo and a “preview” build running on a physical iPhone, how do you debug a problem like this?