Sorry, I was confused as to which product you were using. It’s clear now you have an Ethernet push notification device with the NCD5500 Ethernet module. We have many products called push notification so it can be confusing.
We have not sold these devices in a long time so I never noticed that the NCD5500 module does not have the firmware in it that would append the MAC address into the message packet. This was custom firmware we use to run in the Lantronix XPORT modules if memory serves me correctly.
Try adding a UDP node listening on port 13000. There you should get a string message that contains the MAC address of the module. Once you know the MAC of the device from this packet, as well as it’s IP address, you can use global context variables in Node Red to obtain the device’s MAC address using it’s IP address received on the other node. I know it is not ideal but it is a work around which should work just the same.