Smart TV App ZDF Mediathek - no connection to external

Hi,
I’m searching for some steps on how to trace issues for the German ZDF Mediathek that is running on my LG Smart TV. I’ve got problems with the connection to the app’s server.

The TV is running different apps like ARD Mediathek which is working fine, no connection issues whereas the Pro7 app shows similar connections issue like the one mention above.

Some details: I’m running webproxy (transparent) on green. SquidClamAV is running as well as the URL filter service. The firewalls default mode is blocked for outgoing. IPS is running, QoS and GeoIP blocks all country except those from DE.

For debugging I’ve already disabled WebProxy, URL filter, ClamAV to no avail. Additionally to the mentioned disabled services I’ve set the firewalls mode to allowed. None of those settings used at a time made the ZDF app working.

To narrow down the issue, I’ve set the mode of the FW to blocked again and set up a firewall for the TV’s IP address to destination any for all ports allowed and switched on logging.

To my surprise, no traffic got logged this way. So how would one test such a beast?
Using tcpdump on interface green for the TV’s IP address?
I will get lots of traffic I bet, but which of the packets is the one that get blocked?

Btw, the TV gets its IP address from IPFire DHCP server but even a static one did not change the game.

Thx,
Michael