curl --request POST \
  --url https://api.hubapi.com/conversations/conversations/2026-09-beta/threads/{threadId}/messages \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "type": "MESSAGE",
  "text": "<string>",
  "attachments": [
    {
      "fileId": "<string>",
      "type": "FILE"
    }
  ],
  "recipients": [
    {
      "deliveryIdentifiers": [
        {
          "type": "CHANNEL_SPECIFIC_OPAQUE_ID",
          "value": "<string>"
        }
      ],
      "actorId": "<string>",
      "name": "<string>",
      "recipientField": "<string>"
    }
  ],
  "senderActorId": "<string>",
  "channelId": "<string>",
  "channelAccountId": "<string>",
  "richText": "<string>",
  "subject": "<string>"
}
'

{
  "type": "MESSAGE",
  "id": "<string>",
  "conversationsThreadId": "<string>",
  "createdAt": "2023-11-07T05:31:56Z",
  "createdBy": "<string>",
  "client": {
    "clientType": "HUBSPOT",
    "integrationAppId": 123
  },
  "senders": [
    {
      "actorId": "<string>",
      "deliveryIdentifier": {
        "type": "CHANNEL_SPECIFIC_OPAQUE_ID",
        "value": "<string>"
      },
      "name": "<string>",
      "senderField": "<string>"
    }
  ],
  "recipients": [
    {
      "deliveryIdentifier": {
        "type": "CHANNEL_SPECIFIC_OPAQUE_ID",
        "value": "<string>"
      },
      "actorId": "<string>",
      "name": "<string>",
      "recipientField": "<string>"
    }
  ],
  "archived": true,
  "text": "<string>",
  "attachments": [
    {
      "fileId": "<string>",
      "fileUsageType": "AUDIO",
      "type": "FILE",
      "name": "<string>",
      "url": "<string>"
    }
  ],
  "truncationStatus": "NOT_TRUNCATED",
  "direction": "INCOMING",
  "channelId": "<string>",
  "channelAccountId": "<string>",
  "updatedAt": "2023-11-07T05:31:56Z",
  "richText": "<string>",
  "subject": "<string>",
  "inReplyToId": "<string>",
  "status": {
    "statusType": "FAILED",
    "failureDetails": {
      "errorMessageTokens": {},
      "errorMessage": "<string>"
    }
  }
}