Hey @nado2021 , 

May I know at which step the set-up failed, and what is the Error message on Kasa app? 

Please turn off VPN on your phone during set up, and make sure you have put 100% correct wifi password. 

You could try this troubleshooting guide here first for smart device installation issue: 
https://www.tp-link.com/support/faq/2229/

Hello@nado2021 ,

Thank you for your update.

Please make sure phone is connected to the default SSID ' TP-LINK_Smart _XXXX' at that time or smart device could not be found by Kasa APP. 
(the default SSID has no Internet,which is normal,  and it will disappear after smart device is installed successfully. )

• Manually Connect to TPLINK _ Smart XXX SSID when the app guides to connect to smart Wi-Fi, and go back to Kasa app
• iOS: Go to the Settings page, click on the Wi-Fi option to connect to the Kasa Cam’s Wi-Fi manually.
• Android: Go to the Settings page to connect to the Kasa Cam’s Wi-Fi network. Once it’s connected, please go back to the Kasa app and click on "Try Again".

For IOS14 and above, enable Local network Permission for Kasa app 
https://www.tp-link.com/support/faq/2937/

•  Try a different phone

Hey@nado2021 , 

Glad to hear that the issue is finially resolved, thank you for posting the solution! May I have a chance to know  the APP (the monitoring program ) that affects the plug installation, thank you.