Hello Mario,
As the WS URL is of HTTPs, and as it says you need to use mutual SSL authentication, you need to enable HTTPs port in your PI system.
You can check if it is already enabled by clicking the below link -
https://<host>:5***1
If you are unable to access the above link, then there is no HTTPs port enabled. Please find the below link to setup the HTTPs connection.
http://scn.sap.com/docs/DOC-26145
Regards,
Nitin