Hello  @Demmaka74 

thank you for reaching out to the community. 

May I know do you use Kasa App or use Apple Home app to set up the smart device? 

It is recommended to set up the Homekit device within the Kasa App

Video for Homekit plug or switch: How To Set Up a Kasa HomeKit-Enabled Smart Plug

How to set up your HomeKit-supported Kasa devices

If there is any error message, please check if some tips helps:

HomeKit setup troubleshooting

• Please ensure VPN is OFF on the phone 
• Ensure there is internet access on your phone via Wi-Fi before adding a new device 
• Try to factory reset the device before the configuration.

  @Demmaka74 May I know were you able to set up the smart switch at last? Any update is much appreciated!