$curl = curl_init();
curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://whatstar.gpsritrack.com/api/create-message',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_POSTFIELDS => array(
    'appkey' => 'YOUR_APPKEY',
    'authkey' => 'YOUR_AUTHKEY',
    'to' => '573001234567',
    'message' => 'Hola Ana, su pago de $50 vence el 15/11. Gracias.',
  ),
));
$response = curl_exec($curl);
curl_close($curl);
echo $response;

var request = require('request');
request({
  method: 'POST',
  url: 'https://whatstar.gpsritrack.com/api/create-message',
  formData: {
    appkey: 'YOUR_APPKEY',
    authkey: 'YOUR_AUTHKEY',
    to: '573001234567',
    message: 'Hola Ana, su pago de $50 vence el 15/11. Gracias.'
  }
}, function (error, response) {
  if (error) throw new Error(error);
  console.log(response.body);
});

import requests

url = "https://whatstar.gpsritrack.com/api/create-message"
payload = {
  'appkey': 'YOUR_APPKEY',
  'authkey': 'YOUR_AUTHKEY',
  'to': '573001234567',
  'message': 'Hola Ana, su pago de $50 vence el 15/11. Gracias.',
}
response = requests.post(url, data=payload)
print(response.text)