How to run SIA-DSC on Synology docker/nodered?

I am running NodeRed on a Beaglebone with Debian, and use DCS-SIA to communicate from my Ajax alarm to my Homey which works fine, but since my NAS is running 24/7 anyway, I thought of running it from there. But when I try to run the same flow in a nodered docker, for some reason I can't get the communication working from Ajax to Nodered. (from NR to my homey works fine)
All settings are the same, but when I change the IP in Ajax to my NAS, it keeps disconnected.
Any help greatly appreciated.