Is this a fresh installation of Foreman ?
Was this instance installed with the foreman-installer?
At which point did you get this error?
What version of Foreman are you using.
What plugins?
It would help us a lot if you could provide more information.
This is probably incorrect. The error indicates that your Foreman/Smart Proxy does not trust your Realm provider. You probably need to install your IdM CA cert to your trust store.
Or (bad) disable the verify_ca in the /etc/foreman-proxy/settings.d/realm_freeipa.yml and restart the smart proxy. This should be only used for debugging, otherwise it introduces a security issue.