我第一次嘗試使用 PayPal IPN，但我很難讓它端到端地工作。如果 IPN 響應得到驗證，感謝頁面應顯示視頻。如果未經過驗證（例如，如果有人嘗試直接進入感謝頁面，而不是通過成功的 PayPal 交易），則應顯示一條錯誤消息。在檢查 PayPal 時，我已設法在 IPN 歷史記錄中返回“已發送”狀態，但我的感謝頁面（包含 IPN 驗證器）顯示錯誤 500。錯誤日志表明沒有發布數據發送到該頁面，盡管 PayPal 正在注冊，但它還是成功的。<?php namespace Listener;require('PaypalIPN.php');use PaypalIPN;$ipn = new PaypalIPN();$ipn->useSandbox();$verified = $ipn->verifyIPN();if ($verified) {    echo ("My video will go here");}header("HTTP/1.1 200 OK"); ?>PaypalIPN.php 看起來像這樣：<?phpclass PaypalIPN{/** @var bool Indicates if the sandbox endpoint is used. */private $use_sandbox = false;/** @var bool Indicates if the local certificates are used. */private $use_local_certs = true;/** Production Postback URL */const VERIFY_URI = 'https://ipnpb.paypal.com/cgi-bin/webscr';/** Sandbox Postback URL */const SANDBOX_VERIFY_URI = 'https://ipnpb.sandbox.paypal.com/cgi-bin/webscr';/** Response from PayPal indicating validation was successful */const VALID = 'VERIFIED';/** Response from PayPal indicating validation failed */const INVALID = 'INVALID';/** * Sets the IPN verification to sandbox mode (for use when testing, * should not be enabled in production). * @return void */public function useSandbox(){    $this->use_sandbox = true;}/** * Sets curl to use php curl's built in certs (may be required in some * environments). * @return void */public function usePHPCerts(){    $this->use_local_certs = false;}/** * Determine endpoint to post the verification data to. * * @return string */public function getPaypalUri(){    if ($this->use_sandbox) {        return self::SANDBOX_VERIFY_URI;    } else {        return self::VERIFY_URI;    }}/** * Verification Function * Sends the incoming post data back to PayPal using the cURL library. * * @return bool * @throws Exception */public function verifyIPN(){    if ( ! count($_POST)) {        throw new Exception("Missing POST Data");    }