curl --request POST \
  --url https://api.hubapi.com/conversations/v3/custom-channels/{channelId}/messages \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "attachments": [
    {
      "fileId": "<string>",
      "type": "FILE"
    }
  ],
  "channelAccountId": "<string>",
  "recipients": [
    {
      "deliveryIdentifier": {
        "value": "<string>"
      },
      "name": "<string>",
      "senderActorId": "<string>"
    }
  ],
  "senders": [
    {
      "deliveryIdentifier": {
        "value": "<string>"
      },
      "name": "<string>",
      "senderActorId": "<string>"
    }
  ],
  "text": "<string>",
  "timestamp": "2023-11-07T05:31:56Z",
  "associateWithContactId": 123,
  "inReplyToId": "<string>",
  "integrationIdempotencyId": "<string>",
  "integrationThreadId": "<string>",
  "richText": "<string>"
}
'

import requests

url = "https://api.hubapi.com/conversations/v3/custom-channels/{channelId}/messages"

payload = {
    "attachments": [
        {
            "fileId": "<string>",
            "type": "FILE"
        }
    ],
    "channelAccountId": "<string>",
    "recipients": [
        {
            "deliveryIdentifier": { "value": "<string>" },
            "name": "<string>",
            "senderActorId": "<string>"
        }
    ],
    "senders": [
        {
            "deliveryIdentifier": { "value": "<string>" },
            "name": "<string>",
            "senderActorId": "<string>"
        }
    ],
    "text": "<string>",
    "timestamp": "2023-11-07T05:31:56Z",
    "associateWithContactId": 123,
    "inReplyToId": "<string>",
    "integrationIdempotencyId": "<string>",
    "integrationThreadId": "<string>",
    "richText": "<string>"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    attachments: [{fileId: '<string>', type: 'FILE'}],
    channelAccountId: '<string>',
    recipients: [
      {
        deliveryIdentifier: {value: '<string>'},
        name: '<string>',
        senderActorId: '<string>'
      }
    ],
    senders: [
      {
        deliveryIdentifier: {value: '<string>'},
        name: '<string>',
        senderActorId: '<string>'
      }
    ],
    text: '<string>',
    timestamp: '2023-11-07T05:31:56Z',
    associateWithContactId: 123,
    inReplyToId: '<string>',
    integrationIdempotencyId: '<string>',
    integrationThreadId: '<string>',
    richText: '<string>'
  })
};

fetch('https://api.hubapi.com/conversations/v3/custom-channels/{channelId}/messages', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.hubapi.com/conversations/v3/custom-channels/{channelId}/messages",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'attachments' => [
        [
                'fileId' => '<string>',
                'type' => 'FILE'
        ]
    ],
    'channelAccountId' => '<string>',
    'recipients' => [
        [
                'deliveryIdentifier' => [
                                'value' => '<string>'
                ],
                'name' => '<string>',
                'senderActorId' => '<string>'
        ]
    ],
    'senders' => [
        [
                'deliveryIdentifier' => [
                                'value' => '<string>'
                ],
                'name' => '<string>',
                'senderActorId' => '<string>'
        ]
    ],
    'text' => '<string>',
    'timestamp' => '2023-11-07T05:31:56Z',
    'associateWithContactId' => 123,
    'inReplyToId' => '<string>',
    'integrationIdempotencyId' => '<string>',
    'integrationThreadId' => '<string>',
    'richText' => '<string>'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.hubapi.com/conversations/v3/custom-channels/{channelId}/messages"

	payload := strings.NewReader("{\n  \"attachments\": [\n    {\n      \"fileId\": \"<string>\",\n      \"type\": \"FILE\"\n    }\n  ],\n  \"channelAccountId\": \"<string>\",\n  \"recipients\": [\n    {\n      \"deliveryIdentifier\": {\n        \"value\": \"<string>\"\n      },\n      \"name\": \"<string>\",\n      \"senderActorId\": \"<string>\"\n    }\n  ],\n  \"senders\": [\n    {\n      \"deliveryIdentifier\": {\n        \"value\": \"<string>\"\n      },\n      \"name\": \"<string>\",\n      \"senderActorId\": \"<string>\"\n    }\n  ],\n  \"text\": \"<string>\",\n  \"timestamp\": \"2023-11-07T05:31:56Z\",\n  \"associateWithContactId\": 123,\n  \"inReplyToId\": \"<string>\",\n  \"integrationIdempotencyId\": \"<string>\",\n  \"integrationThreadId\": \"<string>\",\n  \"richText\": \"<string>\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://api.hubapi.com/conversations/v3/custom-channels/{channelId}/messages")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"attachments\": [\n    {\n      \"fileId\": \"<string>\",\n      \"type\": \"FILE\"\n    }\n  ],\n  \"channelAccountId\": \"<string>\",\n  \"recipients\": [\n    {\n      \"deliveryIdentifier\": {\n        \"value\": \"<string>\"\n      },\n      \"name\": \"<string>\",\n      \"senderActorId\": \"<string>\"\n    }\n  ],\n  \"senders\": [\n    {\n      \"deliveryIdentifier\": {\n        \"value\": \"<string>\"\n      },\n      \"name\": \"<string>\",\n      \"senderActorId\": \"<string>\"\n    }\n  ],\n  \"text\": \"<string>\",\n  \"timestamp\": \"2023-11-07T05:31:56Z\",\n  \"associateWithContactId\": 123,\n  \"inReplyToId\": \"<string>\",\n  \"integrationIdempotencyId\": \"<string>\",\n  \"integrationThreadId\": \"<string>\",\n  \"richText\": \"<string>\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.hubapi.com/conversations/v3/custom-channels/{channelId}/messages")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"attachments\": [\n    {\n      \"fileId\": \"<string>\",\n      \"type\": \"FILE\"\n    }\n  ],\n  \"channelAccountId\": \"<string>\",\n  \"recipients\": [\n    {\n      \"deliveryIdentifier\": {\n        \"value\": \"<string>\"\n      },\n      \"name\": \"<string>\",\n      \"senderActorId\": \"<string>\"\n    }\n  ],\n  \"senders\": [\n    {\n      \"deliveryIdentifier\": {\n        \"value\": \"<string>\"\n      },\n      \"name\": \"<string>\",\n      \"senderActorId\": \"<string>\"\n    }\n  ],\n  \"text\": \"<string>\",\n  \"timestamp\": \"2023-11-07T05:31:56Z\",\n  \"associateWithContactId\": 123,\n  \"inReplyToId\": \"<string>\",\n  \"integrationIdempotencyId\": \"<string>\",\n  \"integrationThreadId\": \"<string>\",\n  \"richText\": \"<string>\"\n}"

response = http.request(request)
puts response.read_body

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

{
  "message": "Invalid input (details will vary based on the error)",
  "correlationId": "aeb5f871-7f07-4993-9211-075dc63e7cbf",
  "category": "VALIDATION_ERROR",
  "links": {
    "knowledge-base": "https://www.hubspot.com/products/service/knowledge-base"
  }
}