Not sure what a “flic task” is, but that post URL /api/services/scene/turn_on is correct, but as we are unsure exactly what JSON data you are posting along with that URL, we can’t really help.
Copy and paste the exact URL you are using and the JSON Post data so we can better understand the problem.
It is invaluable in testing to ensure you are sending over the correct data to the correct URL. I use it with all my API services to ensure I am not missing anything.
I’m posting {“entity_id”: “scene.nameofscene”} using the Flic iOS App (flic.io), all other services work fine this way, so I’ll probably create a script instead.
I understand that you are able to run scripts, but switching to a script instead of running the scene directly is a workaround and not solving the problem. I would really like it if we could resolve the problem, not only for your purposes, but for others that may be having this issue as well. If there is something wrong with the Flic app communicating with the scene service api call, then it would be nice to know in if there is a possible bug in either Home Assistant or the Flic iOS app.