curl --request POST \
  --url https://api.jtl-cloud.com/erp/salesOrders/{salesOrderId}/lineitems/{salesOrderLineItemId}/files \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'x-tenant-id: <x-tenant-id>' \
  --data '
{
  "FileData": "aSDinaTvuI8gbWludGxpZnk=",
  "FileDataType": "png",
  "FileName": "Attachment FileName"
}
'

import requests

url = "https://api.jtl-cloud.com/erp/salesOrders/{salesOrderId}/lineitems/{salesOrderLineItemId}/files"

payload = {
    "FileData": "aSDinaTvuI8gbWludGxpZnk=",
    "FileDataType": "png",
    "FileName": "Attachment FileName"
}
headers = {
    "x-tenant-id": "<x-tenant-id>",
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {
    'x-tenant-id': '<x-tenant-id>',
    Authorization: 'Bearer <token>',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    FileData: 'aSDinaTvuI8gbWludGxpZnk=',
    FileDataType: 'png',
    FileName: 'Attachment FileName'
  })
};

fetch('https://api.jtl-cloud.com/erp/salesOrders/{salesOrderId}/lineitems/{salesOrderLineItemId}/files', 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.jtl-cloud.com/erp/salesOrders/{salesOrderId}/lineitems/{salesOrderLineItemId}/files",
  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([
    'FileData' => 'aSDinaTvuI8gbWludGxpZnk=',
    'FileDataType' => 'png',
    'FileName' => 'Attachment FileName'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json",
    "x-tenant-id: <x-tenant-id>"
  ],
]);

$response = curl_exec($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.jtl-cloud.com/erp/salesOrders/{salesOrderId}/lineitems/{salesOrderLineItemId}/files"

	payload := strings.NewReader("{\n  \"FileData\": \"aSDinaTvuI8gbWludGxpZnk=\",\n  \"FileDataType\": \"png\",\n  \"FileName\": \"Attachment FileName\"\n}")

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

	req.Header.Add("x-tenant-id", "<x-tenant-id>")
	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.jtl-cloud.com/erp/salesOrders/{salesOrderId}/lineitems/{salesOrderLineItemId}/files")
  .header("x-tenant-id", "<x-tenant-id>")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"FileData\": \"aSDinaTvuI8gbWludGxpZnk=\",\n  \"FileDataType\": \"png\",\n  \"FileName\": \"Attachment FileName\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.jtl-cloud.com/erp/salesOrders/{salesOrderId}/lineitems/{salesOrderLineItemId}/files")

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

request = Net::HTTP::Post.new(url)
request["x-tenant-id"] = '<x-tenant-id>'
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"FileData\": \"aSDinaTvuI8gbWludGxpZnk=\",\n  \"FileDataType\": \"png\",\n  \"FileName\": \"Attachment FileName\"\n}"

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

{
  "Id": 123,
  "SalesOrderLineItemId": 123,
  "SalesOrderId": 123,
  "FileId": 123,
  "FileDataType": "png",
  "Size": "TODO",
  "CreatedAt": "TODO",
  "FileName": "Anhangdateiname"
}