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Doorbird connected to SOPHOS XG

We want to use a Doorbird (https://www.doorbird.com/de/) doorbell video station, connected to the SOPHOS XG via PoE.
We have created a firewall rule for the Doorbird's IP (Allow all Traffic, LAN to WAN).
Nevertheless, we do not receive any push notifications from the doorbell.
We only get a sound when the app is open on the iPhone, but also no push message.
The bell system is also not marked as online on the manufacturer's side (https://www.doorbird.com/checkonline).
As a test, we connected the system directly to the router via a PoE adapter.
Everything then works and the manufacturer also lists the system as online.
So something is still being blocked by the XG.
Does anyone have any ideas? We found a forum post here that deals with the same problem, but with a UTM (https://community.sophos.com/utm-firewall/f/german-forum/113368/doorbird/406180).

Thanks!