curl --request POST \
  --url https://api.e-invoice.be/api/documents/{document_id}/attachments \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: multipart/form-data' \
  --form file=@example-file

const form = new FormData();
form.append('file', '<string>');

const options = {method: 'POST', headers: {Authorization: 'Bearer <token>'}};

options.body = form;

fetch('https://api.e-invoice.be/api/documents/{document_id}/attachments', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

import requests

url = "https://api.e-invoice.be/api/documents/{document_id}/attachments"

files = { "file": ("example-file", open("example-file", "rb")) }
headers = {"Authorization": "Bearer <token>"}

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

print(response.text)

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.e-invoice.be/api/documents/{document_id}/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=\"file\"; filename=\"example-file\"\r\nContent-Type: application/octet-stream\r\n\r\n<string>\r\n-----011000010111000001101001--",
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "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;
}

using RestSharp;


var options = new RestClientOptions("https://api.e-invoice.be/api/documents/{document_id}/attachments");
var client = new RestClient(options);
var request = new RestRequest("");
request.AlwaysMultipartFormData = true;
request.AddHeader("Authorization", "Bearer <token>");
request.FormBoundary = "---011000010111000001101001";
request.AddFile("file", "example-file");
var response = await client.PostAsync(request);

Console.WriteLine("{0}", response.Content);

{
  "file_name": "<string>",
  "id": "<string>",
  "file_type": "application/pdf",
  "file_size": 0,
  "file_url": "<string>"
}

{
  "detail": "<string>"
}

{
  "detail": "<string>"
}

{
  "detail": "<string>"
}

{
  "detail": "<string>"
}