PostMessage

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "PostMessage",
  "type": "object",
  "properties": {
    "message": {
      "type": "object",
      "properties": {
        "to_user_id": {
          "type": "integer",
          "description": "User ID of the recipient"
        },
        "thread_id": {
          "type": "integer",
          "description": "Identifier for the thread. Should be blank for new threads,\nbut when replying to an existing message, it should be set to\nthe thread_id of the message being replied to.\n"
        },
        "subject": {
          "type": "string",
          "description": "Subject of the message"
        },
        "body": {
          "type": "string",
          "description": "Body of the message"
        }
      }
    }
  }
}