CocoaPods could not find compatible versions for pod "GoogleUtilities/Environment"

[Zambiorix]

Hello all,

I'm fairly new to Flutter and Firebase, but after installing Firebase to my project following:
https://firebase.google.com/docs/flutter/setup?platform=ios
I ran into problems with my app.

Every time I try to run the app, I get following message:

[!] CocoaPods could not find compatible versions for pod "GoogleUtilities/Environment":
  In snapshot (Podfile.lock):
    GoogleUtilities/Environment (= 7.13.3, ~> 7.7)

  In Podfile:
    firebase_core (from `.symlinks/plugins/firebase_core/ios`) was resolved to 3.5.0, which depends on
      Firebase/CoreOnly (= 11.0.0) was resolved to 11.0.0, which depends on
        FirebaseCore (= 11.0.0) was resolved to 11.0.0, which depends on
          GoogleUtilities/Environment (~> 8.0)


You have either:
 * out-of-date source repos which you can update with `pod repo update` or with `pod install --repo-update`.
 * changed the constraints of dependency `GoogleUtilities/Environment` inside your development pod `firebase_core`.
   You should run `pod update GoogleUtilities/Environment` to apply changes you've made.

I have tried several sollutions, like pod repo update or with pod install --repo-update, but nothing helps.
Not sure what to do next. Before the installation of Firebase, my project ran on both iOS and Android without issues.

Any help, much appreciated

Thanks & Cheers
Gerd