What Discourse version are you on?
Your post raw looks funky here. Can you confirm you wrote this
curl -X POST `https://forum.example.com/posts.json` \
-H “Api-Key: <myKey>” \
-H “Api-Username: nobodyfrm” \
-H “Content-Type: application/json” \
-d ‘{“topic_id”: 553,“raw”: “CSD Limburg `` [date=2025-05-10]`”}’
Or share a video/screenshot of what you are typing in the composer.