[Solved] Trouble posting JSON via Micropub endpoint

I just can’t seem to get post creation working via JSON / Micropub. I’ve tried to follow the guide, but every attempt hits a 500 error.

I’ve whittled down my test case to this, and it still returns a 500 error:

(In reality I’m trying to do this via Ruby, but this CURL example represents what I’m trying to do.)

What (probably very obvious) thing am I missing?

Well, of course I figured it out immediately after posting.

The content key in the payload must be an array. I missed that previously.