Diagnose Offline Dahua VTH Units

I have between two and five Dahua indoor monitors (VTH series) that now show as “offline” in the system interface. I only noticed the issue recently, so I’m not sure whether they all failed together or at different times, but everything else on the Dahua network (VTO door station, NVR, cameras) still appears healthy. The task is straightforward: pinpoint why these VTH units dropped offline and restore them so they once again register as “online,” display live video, and exchange calls normally. What I can provide • Remote access via VPN, TeamViewer, or another secure method • On-site assistance for any power-cycling, cable swaps, or factory resets you instruct • Current IP settings, firmware versions, and screenshots from ConfigTool or SmartPSS What I need from you • Step-by-step diagnosis to confirm power, PoE status, cabling, and network reachability • Verification or correction of each unit’s IP/subnet and registration parameters • Firmware compatibility check between VTH units and the VTO door station • Clear actions to bring every affected monitor back online Acceptance criteria All offline VTH monitors must appear online in ConfigTool/SmartPSS, respond to pings, and successfully place and receive calls from the door station. Let me know your expected turnaround and any preliminary information you need so we can get started right away.