Password is just lowercase letters and numbers, worked fine on my LG Nexus 5. Now I've got a Pixel 3 however, latest app version, it won't sign in. The yellow button does nothing at all once I've entered my email and password.
...so I just tried again once I got home and it worked straight away. Weird. Only thing that's changed is I'm now on a different WiFi connection to the one I was previously using. Don't know if that's a factor.