I've installed the Virtualhere Client on a Windows device and the VH Server on a Raspberry Pi Zero.
Once these are connected to the same network everything is working perfectly.
While using a different network for one of both devices it is not working anymore.
All settings have been adjusted according to the 'manual' present in the following link:
The firewall has been disabled on the Windows side and I made sure that the ip-address is correct (on the server side which connects to the client side).
Reverse client was set through the Client and accepted by the Server (I conclude that TCP access is available thus).
Looking forward to any solutions!