curl --request POST \
  --url https://{companyName}.api.joinluminous.com/external/api/v1/export-templates/validate \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "type": "packing_slip",
  "fields": {
    "render_mode": "html",
    "page": {
      "size": "A4",
      "orientation": "Portrait"
    },
    "headerHtml": "<h1>Packing Slip #{{orderNumber}}</h1>",
    "itemsHeaderHtml": "<tr><th>SKU</th></tr>",
    "itemRowHtml": "{{#orderLines}}<tr><td>{{sku}}</td></tr>{{/orderLines}}",
    "footerHtml": "<div>{{fakeField}}</div>"
  }
}
'

import requests

url = "https://{companyName}.api.joinluminous.com/external/api/v1/export-templates/validate"

payload = {
    "type": "packing_slip",
    "fields": {
        "render_mode": "html",
        "page": {
            "size": "A4",
            "orientation": "Portrait"
        },
        "headerHtml": "<h1>Packing Slip #{{orderNumber}}</h1>",
        "itemsHeaderHtml": "<tr><th>SKU</th></tr>",
        "itemRowHtml": "{{#orderLines}}<tr><td>{{sku}}</td></tr>{{/orderLines}}",
        "footerHtml": "<div>{{fakeField}}</div>"
    }
}
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({
    type: 'packing_slip',
    fields: {
      render_mode: 'html',
      page: {size: 'A4', orientation: 'Portrait'},
      headerHtml: '<h1>Packing Slip #{{orderNumber}}</h1>',
      itemsHeaderHtml: '<tr><th>SKU</th></tr>',
      itemRowHtml: '{{#orderLines}}<tr><td>{{sku}}</td></tr>{{/orderLines}}',
      footerHtml: '<div>{{fakeField}}</div>'
    }
  })
};

fetch('https://{companyName}.api.joinluminous.com/external/api/v1/export-templates/validate', 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://{companyName}.api.joinluminous.com/external/api/v1/export-templates/validate",
  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([
    'type' => 'packing_slip',
    'fields' => [
        'render_mode' => 'html',
        'page' => [
                'size' => 'A4',
                'orientation' => 'Portrait'
        ],
        'headerHtml' => '<h1>Packing Slip #{{orderNumber}}</h1>',
        'itemsHeaderHtml' => '<tr><th>SKU</th></tr>',
        'itemRowHtml' => '{{#orderLines}}<tr><td>{{sku}}</td></tr>{{/orderLines}}',
        'footerHtml' => '<div>{{fakeField}}</div>'
    ]
  ]),
  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://{companyName}.api.joinluminous.com/external/api/v1/export-templates/validate"

	payload := strings.NewReader("{\n  \"type\": \"packing_slip\",\n  \"fields\": {\n    \"render_mode\": \"html\",\n    \"page\": {\n      \"size\": \"A4\",\n      \"orientation\": \"Portrait\"\n    },\n    \"headerHtml\": \"<h1>Packing Slip #{{orderNumber}}</h1>\",\n    \"itemsHeaderHtml\": \"<tr><th>SKU</th></tr>\",\n    \"itemRowHtml\": \"{{#orderLines}}<tr><td>{{sku}}</td></tr>{{/orderLines}}\",\n    \"footerHtml\": \"<div>{{fakeField}}</div>\"\n  }\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://{companyName}.api.joinluminous.com/external/api/v1/export-templates/validate")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"type\": \"packing_slip\",\n  \"fields\": {\n    \"render_mode\": \"html\",\n    \"page\": {\n      \"size\": \"A4\",\n      \"orientation\": \"Portrait\"\n    },\n    \"headerHtml\": \"<h1>Packing Slip #{{orderNumber}}</h1>\",\n    \"itemsHeaderHtml\": \"<tr><th>SKU</th></tr>\",\n    \"itemRowHtml\": \"{{#orderLines}}<tr><td>{{sku}}</td></tr>{{/orderLines}}\",\n    \"footerHtml\": \"<div>{{fakeField}}</div>\"\n  }\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://{companyName}.api.joinluminous.com/external/api/v1/export-templates/validate")

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  \"type\": \"packing_slip\",\n  \"fields\": {\n    \"render_mode\": \"html\",\n    \"page\": {\n      \"size\": \"A4\",\n      \"orientation\": \"Portrait\"\n    },\n    \"headerHtml\": \"<h1>Packing Slip #{{orderNumber}}</h1>\",\n    \"itemsHeaderHtml\": \"<tr><th>SKU</th></tr>\",\n    \"itemRowHtml\": \"{{#orderLines}}<tr><td>{{sku}}</td></tr>{{/orderLines}}\",\n    \"footerHtml\": \"<div>{{fakeField}}</div>\"\n  }\n}"

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

{
  "data": {
    "valid": true,
    "errors": [],
    "warnings": []
  }
}

{
  "message": "<string>"
}

{
  "data": {
    "valid": false,
    "errors": [
      "The fields.page.size field is required when fields.render_mode is html."
    ],
    "warnings": [
      "Unknown placeholder {{fakeField}} in footerHtml (not in catalogue for packing_slip)"
    ]
  }
}