ios – Doable to make use of .xcconfig values with GoogleSerive-Data.plist?

I’ve some xcconfig information setting completely different values for Dev, Stage, & Prod environments.

It is working when used at the side of Data.plist, nevertheless I wish to lengthen it to make use of it with GoogleService-Data.plist (as I’m utilizing completely different Firebase shops for various environments). However its not working with GoogleService-Data.plist, for instance in an xcconfig file I’ve outlined:

FIREBASE_API_KEY = AIzaSyCR2X-bvYU0Zuf_uaoQXzGZqYSUbNbvCZ4

Then in GoogleService-Data.plist I’ve:

<dict>
    <key>API_KEY</key>
    <string>$(FIREBASE_API_KEY)</string>

Nonetheless when the app is run, there may be an exception in Firebase as the worth for API_KEY has not been set to that within the .xcconfig.

Why does the substitution work for Data.plist information however not for GoogleService-Data.plist information?