Check the ethernet cable for continuity and correct RJ45 wiring
Often if you get the wires crossed on either side of the RJ45 terminal of the ethernet cable, it will prevent the intercom from getting any internet, even if it shows as powered on over POE. Confirm that your wiring is correct on both ends of the cable and that the RJ45 is correctly wired up.
Cat 6 Wiring Diagram
You can use either A or B style wiring, although B is more common.