FYI "vRO" means vRealize Orchestrator. "vROps" means vRealize Operations Manager.
You can't access vRBC directly in a browser, you must go through the portal in vROps because vRBC does not have a built-in identity manager.
You need vIDM for vRB regardless if you access it through vrops or not.
There are 2 supported deployments
1 deployed with vRA ( vRA has vIDM built in to it so you use its vIDM for access)
2 deployed with vIDM (this is if you dont have vRA)
either way when you register vRB with vIDM it creates 3 groups that you use to give access to vRB
As for your error i did get it with one of my deployments but cant remember the fix. Try using the DNS name instead of the IP