!] CocoaPods could not find compatible versions for pod ..

[!] CocoaPods could not find compatible versions for pod "Firebase/CoreOnly":
  In Podfile:
    firebase_core (from `.symlinks/plugins/firebase_core/ios`) was resolved to 2.22.0, which depends on
      Firebase/CoreOnly (= 10.17.0)

None of your spec sources contain a spec satisfying the dependency: `Firebase/CoreOnly (= 10.17.0)`.

You have either:
 * out-of-date source repos which you can update with `pod repo update` or with `pod install --repo-update`.
 * mistyped the name or version.

이때
pod repo update
하고
pod install
하면 된다

만약 안될시 Podfile.lock 삭제후 pod install을 해보자!