Why the Flutter phone authentication won't work my real device

Question

I have encountered a strange problem. I'm using the Flutter tool to create my iOS app which requires Firebase phone authentication. I was able to make it work on the other app platform without any fuss, but I'm not able to make it work on iOS real device. As per the documentation, I have to register an APN key from the developer account which I did and added my app's bundle ID too. This key I had to upload in my app console in Firebase which I also did. The REVERSE_CLIENT_ID was entered in the project settings in Xcode too, so the simulator version works flawlessly.

However, when it came to make it work on the real iPhone, I get this issue

flutter: exception code verifyPhoneNumberError message Invalid token.

I just am not able to make out what the issue is. One thing to note is that I had created a native Swift version using same APN key with different App ID for test purpose. Could this be a cause? Should I create a new APN key and will that allow my old App ID?

Answer 1

I got it working by doing a couple of things. I don't really know which one is the actual reason of it working, but along with official docs, I also followed this blog post https://medium.com/flutter-community/flutter-adding-sign-in-with-google-and-phone-authentication-to-your-app-69f681518f9b for help and achieved it due to the blogger's additional help when asked.

Basically I created a new APN key altogether for both push notifications and Firebase phone authentication, then uploaded in Firebase console (removing my old one). Later, the blogger suggested I also enable Background modes for remote notifications in my Xcode project settings. I didn't know this, as I had thought the Push Notifications switch was enough. Anyhow, bam! it started working.