iOS framework addition failed due to a Cocoapods installation failure.

I've been trying to build my Unity game to iOS with Admob, Unity IAP, and Firebase Analytics.

• Unity Version: 5.6.2f1 Personal

After importing all the packages, putting the GoogleMobileAds.framework in the Assets/Plugins/iOS folder, I get this error. Anyone know how to resolve it? I've tried uninstalling and reinstalling Cocoapods (using commands from the blog below). But I still get the error. Anything else I can try?...

iOS framework addition failed due to a Cocoapods installation failure.