Micropub: action=update not implemented

[cweiske]

While trying to do this:

Add another category to an existing note via micropub

$ curl -i -X POST -H 'Content-Type: application/json' -H 'Authorization: Bearer abc' --data '{"action":"update","url":"http:\/\/known.bogo\/2016\/this-is-a-slugtest","add":{"category":["foo","bar"]},"replace":{"slug":["differentslug"]}}' 'http://known.bogo/micropub/endpoint'
HTTP/1.1 500 Internal Server Error
...
Couldn't create note

I encountered this error:

HTTP/1.1 500
Couldn't create note