Facebook reviews apps, in your case, the user_location permission, by seeing how your app is using the permission through test users. If there's a test user that works for you, please submit with these credentials, step by step instructions as well as detailed screenshots so reviewers can replicate this process. Once the review team understands how your app is using this permission, your app can now pull ANYONE'S location. You can read more about test users here: https://developers.facebook.com/docs/apps/test-users
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Thanks for clarifying. Technically, your app doesn't have to be "live." It just needs full functionality and real-environment UI and able to demonstrate how it is using the Facebook's permissions. Instead of submitting it onto the iTunes store, Facebook also reviews your app through a sim build: https://developers.facebook.com/docs/ios/creating-ios-simulator-build-for-review. Once this is approved, then deploy your app. This way, your users won't have a bad experience. I hope that answers your question. If not, let me know where you're unclear and I'll try to clarify.