Q:

Can't install pod in iOS app with Firebase

I am not able to successfully install pods to my project.  I am always getting this error:

This is my Podfile (I added FirebaseFirestoreSwift but even when I undo the changes, its still not working):

It was working fine a month ago. 

A:

You need to install the latest version of Xcode command line tools using xcode-select --install.  If you already have an installed version, you might get an error similar to 
xcode-select: error: command line tools are already installed, use "Software Update" to install updates

In that case, try removing the old command line tools from /Library/Developer/CommandLineTools and reinstall it again. 