Updating topic body via the API

I’m trying to update a topic body via the API, but I’m not sure how to do it.

I tried to use POST /posts/ and providing it with the topic_id which only creates a new post for a topic.

I also tried PUT /posts/:id but providing it with the topic id doesn’t update the topic. I actually get a 403.

PUT /t/:slug/:id doesn’t seem to be what I’m looking for.

Any advice here, please?