send.php

$client = new http\Client;
$request = new http\Client\Request;

$body = new http\Message\Body;
$body->append('{
  "message": "Hey {firstName},\\nIt was great meeting you last week at the party. We'd love to have you back at the next one!\\n\\nBest,\\n-Jackie",
  "handwriting": <STRING - handwriting id>,
  "card": <STRING - stationery id>,
  "recipients": [
    {
      "firstName": "Ze",
      "lastName": "Dude",
      "company": "Unemployed",
      "street1": "25 Main Street",
      "city": "Los Angeles",
      "state": "CA",
      "zip": "90210"
    }
  ],
  "from": {
    "firstName": "Jackie",
		"lastName": "Treehorn",
    "street1": "1 Random Street",
    "street2": "Apt 33A",
    "city": "Malibu",
    "state": "CA",
    "zip": "90263"
  }
}');

$request->setRequestUrl('https://api.handwrite.io/v1/send');
$request->setRequestMethod('POST');
$request->setBody($body);

$request->setHeaders(array(
  'content-type' => 'application/json',
  'authorization' => '<your secret key>'
));

$client->enqueue($request)->send();
$response = $client->getResponse();

echo $response->getBody();