Fabric failed to download settings Error Domain=FABNetworkError Code=-5

I found what was wrong. I tried to use the old interface for the crash reports long ago and I have forgotten the script I have placed in Target/Build Phases. When I removed it, everything was fine.

I ran into this problem when I migrated Fabric Crashlytics to Firebase Crashlytics. If you are migrating you need to make sure that you keep the old initialisation logic i.e. make sure that you still have the old initialisation code:

// Objective-C
[FIRApp configure];
[Fabric with:@[CrashlyticsKit]]; // I had removed the this line

// Swift 4
FirebaseApp.configure()
Fabric.with([Crashlytics.self])

You also need to make sure to retain API Key and Build secret in the run script and keep the API Key in your Info.plist.

I had mistakenly removed these things after following the Firebase (non-migration) installation instructions.

Here's a link to the official installation instructions

I had my Crashliticy linked to Fabric. That deactivates crashlytics. Under the Firebase project settings I unlinked crashlytics from fabric. Then logout/login again. Then Crashlytics started with the installation process.