ADFS 4.0 (2016) – User prompted for Windows Credentials when Choosing Claims Provider For Authentication

I have an outside org, this org is setup as a claims provider trust within our ADFS. When a user from this org accesses our IdP initiated sign on page – they hit sign on. They are then brought to the Home Realm Discovery page where they choose the claims provider. They are then prompted for Windows Integrated Authentication from our ADFS environment.

What I’m trying to figure out is why are they not being re-directed to their IdP.

What am I missing here.


Source: Windows Questions