I tried both the custom action URL as well as the default URL *.firebaseapp.com/__/auth/handler, but no luck.
Both cases show the same error on the screen after clicking the link.
It says "The requested action is invalid."
Also I checked the console log, it says "Request is missing required data".
I also checked my GCP admin panel, and make sure there is no restriction to the browser key.
Where could possibly go wrong? Any help is appreciated ??