Try deleting the device in the Kasa App and rediscovering and see it works after that. @DEcosse That worked for me. Fixed in Alexa. Thx. (I'd like to keep everything local in HomeAssistant, but too...

Dimmer works via Kasa app; Power on/off works via Alexa (app and voice-command with Echo); Dimming does not work via Alexa (app and voice)