1) our ssms satellite listens to a completely different url https://<hostname>/Transportgateway/services/DeviceRequestHandler
2) read the release notes of Prime 3.8 en ssms for version compatibility
3) there may be an ACL/firewall in the path between Prime and the sattelite that blocks port 443 (https) and allows port 8443?
Smart Call-Home URL: Smart-enabled product instances need to be configured to send the registration request to SSM On-Prem. This is accomplished by setting the destination http URL in the Smart Call-Home configuration section of product configuration. The URL should be set to;
https://:/Transportgateway/services/DeviceRequestHandler http://:/Transportgateway/services/DeviceRequestHandler.