Google sql不插入

MySQL . 这个 PHP 表单似乎并没有执行,所以并没有SQL insert语句在工作,但我看不出原因——直到昨天它还可以正常工作。这是我的建议 PHP 代码:

if(isset($_POST['email'])){
    $dsn = getenv('MYSQL_DSN');
    $user = getenv('MYSQL_USER');
    $password = getenv('MYSQL_PASSWORD');
    $pdo = new PDO($dsn, $user, $password);

    $email = $_POST['email'];
    syslog(LOG_INFO, 'EMAIL: ' . $email);

    $referral = "";

    if (filter_var($email, FILTER_VALIDATE_EMAIL)) {

        $stmt = $pdo->prepare("INSERT INTO testEmails (email, referral) VALUES (:email, :referral)");

        if(isset($_POST['referral'])){
            $referral = filter_var($referral, FILTER_SANITIZE_STRING);
        }
        else{
            $referral = NULL;
        }

        $stmt->bindParam(':email', $email);
        $stmt->bindParam(':referral', $referral);
        $stmt->execute();

        echo "DONE";
    }
}

我补充说 sysLog 跟踪输入的电子邮件,并且在日志中未显示任何电子邮件 Google Cloud Platform