@herisuryatno2 

Hi,
1. You can refer to the below instructions to troubleshoot the reported issue.
What to do if I can't control my Tapo cameras on the Tapo app?
 

2. If it does not help, please try to factory reset the camera, enable a hotspot Wi-Fi on your phone, reconfigure the camera with a different phone, connect it to the hotspot Wi-Fi, and check if you can control it remotely.

It's unable to downgrade the camera's firmware, however, the latest firmware of the Tapo C520WS is 1.2.10. If your camera is online after connecting to the hotspot Wi-Fi, you can update the firmware for a try.

Best Regards

  @NSoji 

Hi,
Please try to factory reset the camera, enable a hotspot Wi-Fi on your phone, reconfigure the camera with a different phone, connect it to the hotspot Wi-Fi, and check if you can control it remotely.

If yes, the problem may be related to your home Wi-Fi network. You can try to change the DNS server on your router, disable the features such as Firewall rules, Access Control, and Parental Control entries on your home router if there is one, and then reboot the router.

Best Regards