KepServerEX v6.1 to Thingworx v9.3 could not initialize a secure socket connection

I'm having problems connecting KepserverEX v6.1 to Thingworx v9.3

I can confirm that the pc that kepware is installed on can see the Thingworx server (I'm able to access composer and port query confirms port 443 is open). Thingworx’s Industrial Thing’s Base Thing Template is set to “IndustrialGateway” and the appkey is correct. I have also tried both Host name and IP of the server.

This issue is effecting 2x clients both running kepserver v6.1, the reason for the low version number is that both clients were setup 5 years ago to run an Etch line and Penetrant line and we are only now wanting to connect them to Thingworx. Unfortunatly the OEM who did the initial install has gone bust so I'm unable to raise suport ticket via them