Thanks Todd,
I temporarly opened all ports(not ideal) to test, but received the same error. I suspect the issue is hidden within DCM4CHEE/Horos somewhere. I'm running the secured UI and secured Restful services with Keycloak. I'm wondering if that would hold any bearing on the connectivity issues. I did, however configure the OIDC access token for external applications.
I tested Horos with Orthanc and Conquest to see if its an issue with other servers, Orthanc fails to verify, which is more related to Orthanc and Conquest works with no issues.
I've configured the Horos AET in dcm4chee to be the association acceptor/initiator and also as a webb app in dcm4chee-arc device, are there any other places to configure that I may have missed?
Will continue to dig...
Thanks again