{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "#/components/schemas/MessageRequest",
  "title": "MessageRequest",
  "type": "object",
  "required": [
    "message_type",
    "to",
    "from",
    "channel"
  ],
  "properties": {
    "message_type": {
      "type": "string",
      "enum": [
        "text",
        "image",
        "audio",
        "video",
        "file",
        "template",
        "custom"
      ]
    },
    "to": {
      "type": "string",
      "description": "Recipient phone number or ID."
    },
    "from": {
      "type": "string",
      "description": "Sender number or ID."
    },
    "channel": {
      "type": "string",
      "enum": [
        "sms",
        "whatsapp",
        "messenger",
        "viber_service",
        "mms",
        "rcs"
      ]
    },
    "text": {
      "type": "string",
      "description": "Message text (for text messages)."
    },
    "image": {
      "type": "object",
      "description": "Image content (for image messages).",
      "properties": {
        "url": {
          "type": "string"
        },
        "caption": {
          "type": "string"
        }
      }
    }
  }
}