Sorry I forgot BlueSky exists.
What are you using to log in? Your Google account or your Google Play Games account? They're separate. It logs you in with Google Play Games by default. I had this error when I used an emulator and tried logging with Google. Then I used Google Play Games and it worked

Wdym it doesn't recognize it?

Neither Cyril nor Qian really existed back then. He was from nowhere, he was born in a tribe and not a country. To my understanding he traveled from point A (his origin) to point B (where the Tianli resided) and united everything in between under one nation later known as Qian.

Is he not? He literally founded Qian... so I'm assuming he's from an ancient form of Qian and not a different nation.
I was confused as to why his clue is different but guess they made it different cuz there are already a ton of Mountains & Seas characters