Importing the server's certificate to the trusted root store, fixed this issue 
. Now I'm able to communicate with SMP3.0, but still not able to connect to Agentry Server.
I was trying to use the following server address as written here (Agentry client Unable to use localhost with Work Manager in SMP 3.0):
https://server:8081/workmanager (workmanager is my application name)
Using this URL I get the communication error (14). Also tried application id instead (https://server:8081/com.sap.mobile.wm)
None of this is working.
Can anyone tell me how I have to enter the server name in the Agentry Client?
Thanks,
Michel