$> curl -i https://api.sejda.com/v2/html-pdf\
  --fail --silent --show-error \
  --header "Content-Type: application/json" \
  --header "Authorization: Token: api_Y0URAP1K3YH3R3" \
  --data '{"url": "https://airtable.com", "viewportWidth":1200 }' > out.pdf

// npm install request
const request = require('request');
const fs = require('fs');

var opts = {
  uri: 'https://api.sejda.com/v2/html-pdf',
  headers: {
    'Authorization' : 'Token: ' + apiKey,
  },
  json: {
    'url': 'https://airtable.com',
    'viewportWidth': 1200
  }
};

request.post(opts)
  .on('error', function(err){
    return console.error(err);
  })
  .on('response', function(response) {
    if (response.statusCode === 200) {
      response.pipe(fs.createWriteStream('/tmp/out.pdf'))
        .on('finish', function () {
          console.log('PDF saved to disk');
        });
    } else {
      return console.error('Got code: ' + response.statusCode);
    }
  });

import requests

url = 'https://api.sejda.com/v2/html-pdf'
r = requests.post(url, json = {
    'url': 'https://airtable.com',
    'viewportWidth': 1200
  }, headers = {
    'Authorization': 'Token: {}'.format(apiKey)
  })
open('/tmp/out.pdf', 'wb').write(r.content)

<script src="//www.sejda.com/js/sejda-js-api.min.js"></script>
<script>
  document.getElementById('downloadPdfBtn')
    .addEventListener('click', function(e){
      SejdaJsApi.htmlToPdf({
        filename: 'out.pdf',
        /* leave blank for one long page */
        pageSize: 'a4',
        publishableKey: 'api_public_y0urap1k3yh3r3',
        htmlCode: document.querySelector('html').innerHTML,
        /* url: window.location.href */
        always: function(){
          // PDF download should have started
        }
      });
    })
</script>
/* Don't forget to configure your API Allowed domains, on your account page. */

<!-- Maven dependency -->
<dependency>
  <groupId>org.apache.httpcomponents</groupId>
  <artifactId>httpclient</artifactId>
	<version>4.5.8</version>
</dependency>

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;

CloseableHttpClient httpClient = HttpClientBuilder.create().build();
HttpPost request = new HttpPost("https://api.sejda.com/v2/html-pdf");
request.setHeader(HttpHeaders.AUTHORIZATION, "Token: " + apiKey);
request.setEntity(new StringEntity(
    "{\"url\": \"https://airtable.com\", \"viewportWidth\":1200 }",
    ContentType.APPLICATION_JSON));

HttpResponse response = httpClient.execute(request);
if (response.getStatusLine().getStatusCode() == 200) {

    try (InputStream in = response.getEntity().getContent();
         OutputStream out = new FileOutputStream(new File("/tmp/out.pdf"))) {
        byte[] buffer = new byte[8 * 1024];
        int bytesRead;
        while ((bytesRead = in.read(buffer)) != -1) {
            out.write(buffer, 0, bytesRead);
        }
    }
}

$url = "https://api.sejda.com/v2/html-pdf";
$content = json_encode(array('url' => 'https://airtable.com'));

$curl = curl_init($url);
curl_setopt($curl, CURLOPT_HEADER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

curl_setopt($curl, CURLOPT_HTTPHEADER, array(
  "Content-type: application/json",
  "Authorization: Token: " . $apiKey));

curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $content);

$response = curl_exec($curl);

$status = curl_getinfo($curl, CURLINFO_HTTP_CODE);

if ($status == 200) {
  $fp = fopen("out.pdf", "w");
  fwrite($fp, $response);
  fclose($fp);
  print("PDF saved to disk");
} else {
  print("Error: failed with status $status, response $response, curl_error " . curl_error($curl) . ", curl_errno " . curl_errno($curl));
}

using System.Net.Http;
using Newtonsoft.Json.Linq;

var baseUrl = "https://api.sejda.com/v2/html-pdf";

using (var client = new HttpClient())
{
  client.DefaultRequestHeaders.TryAddWithoutValidation(
      "Authorization", "Token: " + apiKey
  );

  var json = new JObject();
  json.Add("url", "https://airtable.com");
  json.Add("viewportWidth", 1200);
  //json.Add("htmlCode", File.ReadAllText(@"c:\doc.html", Encoding.UTF8));

  var content = new StringContent(json.ToString(), Encoding.UTF8, "application/json");

  using (var res = await client.PostAsync(baseUrl, content))
  {
    var statusCode = (int)res.StatusCode;

    if (statusCode == 200)
    {
      var httpStream = await res.Content.ReadAsStreamAsync();
      var outputFilePath = Path.GetTempFileName();
      using (var fileStream = File.Create(outputFilePath))
      using (var reader = new StreamReader(httpStream))
      {
        httpStream.CopyTo(fileStream);
        fileStream.Flush();
      }
      // outputFilePath contains the PDF output
    }
    else
    {
      // retry, then handle error
      throw new Exception("Unexpected response code: " + statusCode);
    }
  }
}