@RinChui Good day, 

Thank you for your valuable feedback, here are some suggestions and feel free to let us know if it works for you. 

Step 1

Check the network diagram of the home network, make sure the Kasa Cam is not connected to a range extender.

Step 2

Change the DNS server on the router to 8.8.8.8 for a try.

Step 3

Disable the firewall and Antivirus settings on the router and modem.

Step 4

Check if there are any advanced settings on the router blocking the Kasa Cam, such as Access Control.

If issue persists, can you help confirm some details here:
-Did you try to watch the video clip within 2 days, may I have a photo of the Error message? 

-the model of your wifi router :
-How about your network topology:
-Model of your phone and its IOS / Android version:
- Tapo app version (make sure its up to date )