Linker command failed with exit code 1 -- Firebase

First Install FireBase properly via CocoaPods. Try the following steps

Step 1 - Quit the Xcode. (Don't just close the Xcode window, right click and Quit it explicitly).

Step 2 - Clear your derived data. You can find your derived data in here

~/Library/Developer/Xcode/DerivedData

Step 3 - Open your .xcworkspace, Not .xcproject

Step 4 - Clean your project by pressing ⌘+Shift+K keys

Step 5 - Build your project by pressing ⌘+B keys

Make sure you're opening the .xcworkspace and not the .xcproject file in Xcode. Close the project and open .xcworkspace