ProSys OPCUA Server failed to register to my LDS

Question

I wrote an application for an LDS using Milo SDK. I implemented the onRegisterServer service set and when I start up my Prosys Simulator Server and specify the endpoint for which it should register itself to, I get this error in the simulation log files:

  registerToDiscoveryServer=true
  07/25/2022 13:37:12.338 WARN  [a STARTING]                      
 com.prosysopc.ua.server.aq  [] - Could not register server (offline) to Discovery 
Server at opc.tcp://localhost:4840/UADiscovery/discovery Cause: Failed to retrieve 
endpoints. The server is not available: opc.tcp://localhost:4840/UADiscovery/discovery 
07/25/2022 13:37:15.018 WARN  [b STARTING]                      
com.prosysopc.ua.server.aq  [] - Could not register server (online) to Discovery 
Server at opc.tcp://localhost:4840/UADiscovery/discovery Cause: Failed to retrieve 
endpoints. The server is not available: opc.tcp://localhost:4840/UADiscovery/discovery

Do I have to implement onGetEndpoints in addition to the onRegisterServer? The UaStackServer in Milo already implements it so I am kind of confused as to why this is not working.