您需要的是ipn（即时付款通知）。您可以在这里找到更多信息，也可以在这里找到一些php示例代码
基本上，您可以在表单中指定一个url，在那里您可以在支付完成后获得通知，在那里您可以更新您的数据库。

paypalipn.php说：

<?php
    class 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");
            }
            $raw_post_data = file_get_contents('php://input');
            $raw_post_array = explode('&', $raw_post_data);
            $myPost = array();
            foreach ($raw_post_array as $keyval) {
                $keyval = explode('=', $keyval);
                if (count($keyval) == 2) {
                    // Since we do not want the plus in the datetime string to be encoded to a space, we manually encode it.
                    if ($keyval[0] === 'payment_date') {
                        if (substr_count($keyval[1], '+') === 1) {
                            $keyval[1] = str_replace('+', '%2B', $keyval[1]);
                        }
                    }
                    $myPost[$keyval[0]] = urldecode($keyval[1]);
                }
            }
            // Build the body of the verification post request, adding the _notify-validate command.
            $req = 'cmd=_notify-validate';
            $get_magic_quotes_exists = false;
            if (function_exists('get_magic_quotes_gpc')) {
                $get_magic_quotes_exists = true;
            }
            foreach ($myPost as $key => $value) {
                if ($get_magic_quotes_exists == true && get_magic_quotes_gpc() == 1) {
                    $value = urlencode(stripslashes($value));
                } else {
                    $value = urlencode($value);
                }
                $req .= "&$key=$value";
            }
            // Post the data back to PayPal, using curl. Throw exceptions if errors occur.
            $ch = curl_init($this->getPaypalUri());
            curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
            curl_setopt($ch, CURLOPT_POST, 1);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, $req);
            curl_setopt($ch, CURLOPT_SSLVERSION, 6);
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
            curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
            // This is often required if the server is missing a global cert bundle, or is using an outdated one.
            if ($this->use_local_certs) {
                curl_setopt($ch, CURLOPT_CAINFO, __DIR__ . "/cert/cacert.pem");
            }
            curl_setopt($ch, CURLOPT_FORBID_REUSE, 1);
            curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
            curl_setopt($ch, CURLOPT_HTTPHEADER, array(
                'User-Agent: PHP-IPN-Verification-Script',
                'Connection: Close',
            ));
            $res = curl_exec($ch);
            if ( ! ($res)) {
                $errno = curl_errno($ch);
                $errstr = curl_error($ch);
                curl_close($ch);
                throw new Exception("cURL error: [$errno] $errstr");
            }
            $info = curl_getinfo($ch);
            $http_code = $info['http_code'];
            if ($http_code != 200) {
                throw new Exception("PayPal responded with http code $http_code");
            }
            curl_close($ch);
            // Check if PayPal verifies the IPN data, and if so, return true.
            if ($res == self::VALID) {
                return true;
            } else {
                return false;
            }
        }
    }

看来我必须改变很多参数才能做到这一点

从你的问题和附加的代码来看，你需要一些解释它应该如何工作
您需要执行以下步骤：
首先创建您自己的表单并从客户端收集数据，然后将其存储在您的数据库中（使status not pay yet..），并将表单发送到第二页
在这个页面上有一个贝宝购买按钮，你将打印到客户信息从数据库到贝宝购买按钮的形式
在返回页或notify\u url上，请查看这里的paypal响应，如果支付成功，请添加db行并更改用户状态。
发送至感谢页面