I am running a TS3 server on my Qnap NAS but I can't connect to it from any of my iOS devices (iPad, iPhone) using the paid app.
The devices can connect to other TS3 server, but NOT to "ferenc.hopto.org". The server works fine from my PC and my friends from several other contries are able to connect to it as well from their computers.
Could someone help me figure out why this is happening?

Thank you in advance.