当我尝试在android中注册PHP页面时，PHP得到错误消息

PFB代码。DB连接是成功的，但当尝试在我的android手机注册register.php脚本获得错误页面或获得请填写所有值。我没有获得成功。请帮助。我也使用URL注册URL在我的java代码以及http://xxxx/Userregistration/register.php。

register.php

<?php
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    $name = $_POST['name'];
    $username = $_POST['username'];
    $password = $_POST['password'];
    $email = $_POST['email'];
    if ($name == '' || $username == '' || $password == '' || $email == '') {
        echo 'please fill all values';
    } else {
        require_once('dbConnect.php');
        $sql = "SELECT * FROM KumbhaApp  WHERE username='$username' OR email='$email'";
        $check = mysqli_fetch_array(mysqli_query($con, $sql));
        if (isset($check)) {
            echo 'username or email already exist';
        } else {
            require_once('dbConnect.php');
            $sql = "INSERT INTO KumbhaApp (name,username,password,email) VALUES('$name','$username','$password','$email')";
        }
    }
    if (!preg_match("/^[a-zA-Z ]*$/", $name)) {
        $nameErr = "Only letters and white space allowed";
    } else {
        if (!preg_match("/(['w'-]+'@['w'-]+'.['w'-]+)/", $email)) {
            $emailErr = "Invalid email format";
        }
    }
    if (mysqli_query($con, $sql)) {
        echo 'successfully registered';
        header('Location: securedpage.php');
    } else {
        echo 'oops! Please try again!';
    }
    mysqli_close($con);
}
?>