$api_url =
'https://yourSubDomain.payfull.com/integration/api/v1';    

   $merchantPassword = 'your merchant password';  

                        $params = array(                  
                     "merchant"        => 'your merchant name',
                       "type"            => 'Set',          
                        "set_param"            => 'TrustedClient',
                        "language"            => 'tr',
‍
                       "client_ip"        => '192.168.1.1',
                     "client_firstname"       => 'Muhammed'
                     "client_lastname"       => 'Sahin'
                     "recipient_email"       => 'MuhammedSalihTestEmail@payfull.com'
                     "recipient_phone"       => '009053.........'
                     "title"       => 'payment title here'
                      "start_date"            => '01-09-2016',
                      "end_date"              => '01-01-2030',
                      "changeable_quantity"   => '0',
                      "predefined_payment"    => '0',

                      "payment_item"          => '1',
                      "payment_free_amount"   => '1',
                      "payment_free_title"    => 'Item Title here',

                      "quantity"              => '1',
                      "currency"              => 'TRY',
                      "kdv"                   => '1',
                      "via_email_sms"         => '0',
                      "email_text"            => 'email text come here',
                      "sms_text"              => 'sms text come here',

                      "request_type"          => 'recurring',
                      "request_action_type"   => 'auto',
                      "request_period"        => '1',
                      "repetition_count"      => '2',
     );
                     // Hash kodu üretme yöntemi.
                        ksort($params);
                     $hashString = "";
                     foreach ($params as $key=>$val) {                             
                      $l = mb_strlen($val);  
                      if($l) $hashString .= $l . $val;
                       }


                       $params["hash"] = hash_hmac("sha256", $hashString, $merchantPassword);
// Hash kodu üretilip parametreler arasına "hash" index'i ile eklendi.

//curl sürecini başlatıyoruz.
                       $ch = curl_init();
                       curl_setopt($ch, CURLOPT_URL, $api_url);            
                        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
                        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
                        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);                                               curl_setopt($ch, CURLOPT_TIMEOUT, 60);      
                        curl_setopt($ch, CURLOPT_POST, 1);  
                        curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($params));

//curl için gerekli olan URL değeri ve parametreler hazırlandı ve curl_exec() fonksiyonu ile işlemi başlatıp cevabı $response değerine atıyoruz.

                         $response = curl_exec($ch);                    

           $curlerrcode = curl_errno($ch);
           $curlerr = curl_error($ch);              

           var_dump(json_decode($response));