HttpClient client = new HttpClient();
string key = "YOUR_API_KEY";
string user = "YOUR_PHONE_NUMBER";
string pass = "YOUR_PASSWORD";
string sender = "SENDER";
string recipient = "0512345678; 0512345678"; // Numbers must be separated with ;
string msg = "SMS4FREE"; // can be anything

var requestObject = new
{
key,
user,
pass,
sender,
recipient,
msg
};

var dataAsJson = JsonConvert.SerializeObject(requestObject);
var buffer = Encoding.UTF8.GetBytes(dataAsJson);

var byteContent = new ByteArrayContent (buffer);
byteContent. Headers.ContentType = new MediaTypeHeaderValue("application/json");

var response = client.PostAsync("https://api.sms4free.co.il/ApiSMS/v2/SendSMS", byteContent).Result;
var responseString = response.Content.ReadAsStringAsync().Result;
Console.WriteLine(responseString); // Gives you how many recipients the message was sent to
                        

import requests
url="https://api.sms4free.co.il/ApiSMS/v2/SendSMS"
key="YOUR_API_KEY"
user="YOUR_PHONE_NUMBER"
password="YOUR_PASSWORD"
sender="SENDER"
recipient="0512345678; 0512345678" # Numbers must be seperated with ;
msg="test" # can be anything
data={}
data["key"]=key
data["user"]=user
data["sender"]=sender
data["pass"]=password
data["recipient"]=recipient
data["msg"]=msg

response=requests.post(url, json=data)
print(response.text) #Gives you how many recipients the message was sent to
                                        

$url = "https://api.sms4free.co.il/ApiSMS/v2/SendSMS";
$key = "YOUR_API_KEY";
$user = "YOUR_PHONE_NUMBer";
$pass = "YOUR_PASSWORD";
$sender = "SENDER";
$recipient = "0512345678;0512345678"; // Numbers must be seperated with ;
$msg = "message"; # can be anything

// $postdata =
array(
'key' => $key,
'user' => $user,
'pass' => $pass,
'sender' => $sender,
'recipient' => $recipient,
'msg' => $msg
);
$data_string = json_encode($postdata);

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 0);
curl_setopt($ch, CURLOPT_TIMEOUT, 400);
set_time_limit(0);

$data = curl_exec($ch);
$curl_errno = curl_errno($ch);
$curl_error = curl_error($ch);
curl_close($ch);

if ($curl_errno > 0) {
echo "CURL Error ($curl_errno): $curl_error\n";
} else {
echo "Data received: $data\n"; // Gives you how many recipients the message was sent to
}