Lazım olanlar : Composer, Guzzle

<?php
define("IN_MYBB", 1);
require_once "./global.php";

global $mybb, $db;


if($mybb->user['uid'] <= 0)
        echo "Please login or register";
    else
    {
        $id = $mybb->user['uid'];
        $email =  $mybb->user['email'];
      #  require_once('vendor/autoload.php');

      #  $client = new GuzzleHttp\Client([
      #      'allow_redirects'=>false,
      #  ]);

      #  $res = $client->post('https://oplata.info/asp2/pay.asp', [
      #      'form_params' => [
      #          'Agent' => '' . $id . '',
      #          'product_id' => '11',
      #          'ID_D' => '22',
      #         'seller_id' => '339',
      #          'lang' => 'en-US',
      #          'email' => 'tes@gmail.com',
      #          'TypeCurr' => 'USD',
      #          'FailPage' => 'https://site.com/upgrade.php',
      #          '_ow' => '0',
      #         '_ids_shop' => '123',
      #        '_dga' => 'null'
      #      ]
      #  ]);
        #$a = $res->getBody();
      #  $rest = substr("' . $a . '", 106, -23);
        $redirecturl = "https://www.oplata.info/asp2/pay_wm.asp?lang=en-US&id_d=123&agent=$id&email=$email&failpage=https%3A//test.com/";
        $statusCode = 301;
        header('Location: ' . $redirecturl, true, $statusCode);
        die();
    }


    
?>
Umarım yardımcı olur.