SSO for Second IdP Failing

We are trying to set up a second IdP for SSO. The first IdP is set as default and is working as expected.

When I test the SSO from the second IdP using the "Test Identity Provider" on the Diagnostics and Activation page of the SSO setup, it fails. If I check the Federation logs, I have the following information:

If I set up the same IdP on a different instance as the primary IdP, it works, so it does not seem to be a problem with the IdP. Is there a different setup required for multiple IdPs?

Thank you,