@eddiehk 

Hi,
You can check if the following tips help.
    1. Reboot your router and wait for a moment until it's working.
    2. Make sure the 2.4G Wi-Fi name on the router is different from the 5G, and disable the Antivirus, Firewall rules, MAC Filtering, etc., on the router for a try.
    3. Factory reset the camera and reconfigure it.
    4. If the problem remains, enable a hotspot Wi-Fi on your phone, factory reset the camera, reconfigure it on another phone, connect it to the hotspot Wi-Fi, and then check if the camera will work.
Best Regards

  @eddiehk  Glad to hear your case is solved~