curl --request POST \
  --url https://api.helpdesk.com/v1/transactions/{transactionID}/attachments \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: multipart/form-data' \
  --form agentID=42e113f9-9353-4e89-9f68-69b92f423b0c \
  --form 'attachments=<string>' \
  --form attachments.items='@example-file'

import requests

url = "https://api.helpdesk.com/v1/transactions/{transactionID}/attachments"

files = { "attachments.items": ("example-file", open("example-file", "rb")) }
payload = {
    "agentID": "42e113f9-9353-4e89-9f68-69b92f423b0c",
    "attachments": "<string>"
}
headers = {"Authorization": "Basic <encoded-value>"}

response = requests.post(url, data=payload, files=files, headers=headers)

print(response.text)

const form = new FormData();
form.append('agentID', '42e113f9-9353-4e89-9f68-69b92f423b0c');
form.append('attachments', '<string>');
form.append('attachments.items', '{
  "fileName": "example-file"
}');

const options = {method: 'POST', headers: {Authorization: 'Basic <encoded-value>'}};

options.body = form;

fetch('https://api.helpdesk.com/v1/transactions/{transactionID}/attachments', 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.helpdesk.com/v1/transactions/{transactionID}/attachments",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => "-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"agentID\"\r\n\r\n42e113f9-9353-4e89-9f68-69b92f423b0c\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments\"\r\n\r\n<string>\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments.items\"; filename=\"example-file\"\r\nContent-Type: application/octet-stream\r\n\r\n{\r\n  \"fileName\": \"example-file\"\r\n}\r\n-----011000010111000001101001--",
  CURLOPT_HTTPHEADER => [
    "Authorization: Basic <encoded-value>",
    "Content-Type: multipart/form-data"
  ],
]);

$response = curl_exec($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.helpdesk.com/v1/transactions/{transactionID}/attachments"

	payload := strings.NewReader("-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"agentID\"\r\n\r\n42e113f9-9353-4e89-9f68-69b92f423b0c\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments\"\r\n\r\n<string>\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments.items\"; filename=\"example-file\"\r\nContent-Type: application/octet-stream\r\n\r\n{\r\n  \"fileName\": \"example-file\"\r\n}\r\n-----011000010111000001101001--")

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

	req.Header.Add("Authorization", "Basic <encoded-value>")

	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.helpdesk.com/v1/transactions/{transactionID}/attachments")
  .header("Authorization", "Basic <encoded-value>")
  .body("-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"agentID\"\r\n\r\n42e113f9-9353-4e89-9f68-69b92f423b0c\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments\"\r\n\r\n<string>\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments.items\"; filename=\"example-file\"\r\nContent-Type: application/octet-stream\r\n\r\n{\r\n  \"fileName\": \"example-file\"\r\n}\r\n-----011000010111000001101001--")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.helpdesk.com/v1/transactions/{transactionID}/attachments")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Basic <encoded-value>'
request.body = "-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"agentID\"\r\n\r\n42e113f9-9353-4e89-9f68-69b92f423b0c\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments\"\r\n\r\n<string>\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"attachments.items\"; filename=\"example-file\"\r\nContent-Type: application/octet-stream\r\n\r\n{\r\n  \"fileName\": \"example-file\"\r\n}\r\n-----011000010111000001101001--"

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

[
  {
    "ID": "42e113f9-9353-4e89-9f68-69b92f423b0c",
    "url": "https://example.com",
    "cid": "",
    "name": "",
    "size": 0,
    "type": ""
  }
]