Actions not working

I am trying to use the actions when the output is switched on or off to ensure that the state within Smartthings is correct when manually switching the state of the dimmer. However I am unable to get it to work.

It seems I need to use a GET, however I tried accessing both an endpoint on my local network and when this did not work I even made it available externally. However I can not get it to work. Any ideas ?

Today I tried to configure the same actions on one of my other dimmer2's and they are working with the same url ... I copied the url from the one which did not work and pasted them into the other and that one works. What am I missing here ?

Note: In both cases the Enabled checkbox is marked

After some tries I managed to do a hard-reset on the device and now the state is also correctly reflected in my Smartthings app when I manually change the state of the Shelly device with the switch. So it seemed it was in a weird state.