API を使用して投稿の内容を更新する際に 500 または 400 エラーが発生

Glad you got it figured out! I’ve got a bunch of topics that are me taking to myself.

Mostly these are the docs, and they are continually updated: How to reverse engineer the Discourse API :wink:

I generally forget that there are any docs besides just seeing how it works in the browser development tools.