<?php
require "guzzle/vendor/autoload.php";
use GuzzleHttp\Client;

$client = new Client([
    // Base URI is used with relative requests
    'base_uri' => 'https://sms.standingtech.com/api/v3/sms/',
]);
$now = date("Y-m-d H:i:s");
$body = <<<DATA
{"recipient":"9647xxxxxxxxx",
"sender_id":"Standing",
"type":"plain",
"message":"This is a test message using Guzzle at $now"
}
DATA;

$response = $client->request('POST', 'send', [
'headers' => [
    'Authorization'     => 'Bearer API_KEY',
    'Content-Type'     	=> 'application/json',
    'Accept'     		=> 'application/json',
    ],
//'stream' => true,
'body' => $body,
//'sink' => 'temp.txt',
//'verify' => false,

]);

$response = $response->getBody()->getContents();

echo "<pre>";
print_r(json_decode($response, true));

<?php
$url = "https://sms.standingtech.com/api/v3/sms/send";
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

$headers = array(
   "Authorization: Bearer API_KEY",
   "Content-Type: application/json",
   "Accept: application/json",
);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);

$data = <<<DATA
{"recipient":"9647xxxxxxxxx",
"sender_id":"YourName",
"type":"plain",
"message":"This is a test message"
}
DATA;

curl_setopt($curl, CURLOPT_POSTFIELDS, $data);

//for debug only!
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);

$resp = curl_exec($curl);
curl_close($curl);
var_dump($resp);