We're in final stages of developing a Shopify App, and we realized that when viewed from the smartphone Shopify App (either iOS or Android), the admin of our app won't load. Any browser on any device looks OK, but the official app just shows a blank page. Any piece of advice is much appreciated.
I notice the app also isn't loading in Safari (12.1.1). This could explain why it's not loading on the iOS app. Consider debugging the app in Safari first, which might resolve the issue on all devices.