You can’t use this instance username to login to a different instance. You need to be on Beehaw.org, to use your Beehaw account; you can’t use that to logon to kbin.social.
However, you should be able to see the instance and subscribe to it from Beehaw:
You can’t use this instance username to login to a different instance. You need to be on Beehaw.org, to use your Beehaw account; you can’t use that to logon to kbin.social. However, you should be able to see the instance and subscribe to it from Beehaw:
Search for the URL
Click the resulting link
Click subscribe.