1. Queries must always be sent over a secure connection (HTTPS).


POST requests can be sent either using query string or json. If you send you content as json you have to make sure that header content type is set to json as well.
      
$query = array(
  'subject' => 'Test subject',
  'from' => 'test@example.com',
  'html' => 'https://smaily.com/',
);

// Create query string using php function http_build_query().
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($query));

// Create json string using php function json_encode().
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($query));
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));

     

  

2. Results will be given in JSON.

3. Every query must be authenticated.