Instead of trying to sign on to the OBiTALK dashboard by using a Google user ID/password, instead create a unique OBiTALK user ID and password (and keep track of it!!!).
Once you're signed in, then you can configure Google Voice using your Google account's credentials, as long as you are logged into your Google Voice account in another tab on your web browser.
That error message is because Obihai has some sort of OAUTH 2.0 authentication problem with the portion of their website that is trying to use people's Google credentials as a "single sign-on". If you would like to help get it fixed, you can forward your issue to
support@obihai.com instead of
admin@obihai.com (the address in your error message is just a canned error message).