Can you check your Google Play Services version?
Prerequisites :
One of the reason for this problem could be, your Sign In Method inside Firebase > Auth Dashboard might be disabled.
EDIT
The 10.2.1 version wasn't available for downloading from any (virtual) device that you tested, required update.
The version of Google Play Services shown in the Extras section at the bottom of the Standalone SDK Manager has no effect on the version used by an emulator. The emulators run on system images configured to contain some particular version of Play Services, which is not always the same.
You should confirm that you have downloaded the latest emulator images having version compatibility like version 10.2.1(latest).