type: object
properties:
  meta:
    type: object
    properties:
      labels:
        type: array
        items:
          type: string
      additional_attributes:
        type: object
      contact_id:
        type: number
  payload:
    type: array
    description: 'array of messages'
    items:
      allOf:
        - $ref: '#/definitions/extended_message'