Firebase Undefined symbols for architecture x86_64

Question

I am using firebase as part of a project I am working on in iOS, and I just stumbled upon the following linking error when I try to compile my code against an iPhone 6 or 7

Answer 1

In my case, for using only Firebase Auth and Firebase Firestore, installing with Cocoapods, all I had to do was click the + sign for both Debug and Release sections under Other Linker Flags in Build Settings. The $(inherited) flag was added automatically. Built just fine after that!

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