Cloud save between PC and android? (Solved!)

So I had this game on Steam for quite some time and recently also bought it for Android.

Now I have been playing a week on my cellphone and suddenly all my progress is gone. So far so good (not). Then I see that there is a cloud save feature, so I log into my PC client and register a cloud account and upload my progress...

...now on my cellphone it tells me if I try to login with the same credentials "failed to log in".

What is going wrong here? I am a bit stumped and I don't want to lose a week of progress. Bit demoralized right now.