Send a message to a conversation
content, gif, or a file attachment is required.
For space conversations with postingPermission: "admins", only users with admin or moderator role in the parent Space can send messages.
This endpoint accepts multipart/form-data to support file attachments alongside message content.
user, quotedMessage, files, reactionCounts (empty on creation), and userReactions (empty on creation). If localId was provided, it is echoed in the response.
Empty Message — 400 Bad Request
Forbidden — 403
Invalid Parent — 400 Bad Request