Connecting to OEPAS server from .NET Open Client

My Connection to the OEPAS server from the ABL like this
CONNECT("-sessionModel Session-free -URL localhost:8810:oepas1/apsv")

The documentation for .NET Open Client hasn’t been updated since 2014 (11.4), and the information I can find on the changes to the connection class are very few.

I have got the connection from .NET to work using a connection like
backend = new Connection( "http://localhost:8810/ /apsv",   "", "", "");
 backend.setSessionModel(1);

When I from .NET uses the URL ‘localhost:8810:oepas1/apsv’ I get the following error ‘Bad URL format’.
If I try with ‘localhost:8810/.../apsv’ I get ‘SessionPool: NoAvailableSession [Could not connect to the appserver: General Error 9990. (7203)]’

Does anyone know the correct syntax to connect to a OEPAS server from a .NET project?

Anders