@Emil Thanks, I got it to work now. I had to open the flic app and execute the action manually from within the app. Then it will asks for Local Network permissions. I checked the iOS settings before, but apparently the Local Network switch there only appears after it was requested within the app.

Hi. I'm not familiar with Sonoff, but it seems you can get IFTTT to work. Please check out https://sonoff.tech/sonoff-works-with-ifttt.