View difference between Paste ID: 6nhBX9My and 3QJ5cN1Z

 <?php
 ini_set('display_errors',1); // enable php error display for easy trouble shooting
 error_reporting(E_ALL); // set error display to all
 session_start();
 
 require_once "../../config/db.php";
 
 if(isset($_POST)) {
 
 	// you should validate all inputs and make sure you are getting what you are expecting
 	// first you need to check empty
 	// second you should use strip_tags for all inputs to avoid xss injection
 	// Example: bad user may insert javascript to first name or last name and when you fetch the name, javascript will be loaded
 	// Use FILTER_VALIDATE_EMAIL to validate email address http://php.net/manual/en/filter.filters.validate.php
 	// check if email exists. If exists echo 'Error' with exit
 	// use password_hash instead of MD5 for password http://php.net/manual/en/function.password-hash.php
 	// use prepared statement to prevent sql injection https://stackoverflow.com/questions/60174/how-can-i-prevent-sql-injection-in-php?rq=1
 
 	// to temporary fix your problem
 
 	$check_empty = true;
 
 	foreach ($_POST as $post) {
 		if (empty($post)) {
 			// value is empty
 			$check_empty = false;
 			echo "error";
 			exit;
 		}
 	}
 
 	$first_name = mysqli_real_escape_string($conn, $_POST['first_name']);
 	$last_name = mysqli_real_escape_string($conn, $_POST['last_name']);
 	$email = mysqli_real_escape_string($conn, $_POST['email']);
 	$password = mysqli_real_escape_string($conn, $_POST['password']);
 	$user_birthday = mysqli_real_escape_string($conn, $_POST['user_birthday']);
 	$user_sex = mysqli_real_escape_string($conn, $_POST['user_sex']);
 
 	$password = base64_encode(strrev(md5($password)));
 	$dob = date('Y-m-d',strtotime($user_birthday));
 	if ($check_empty) {
 		$sql = "SELECT email FROM users WHERE email = '$email' LIMIT 1";
 		if ($result = $conn->query($sql)) {
-			if ($result->num_rows() > 0) {
+			if ($result->num_rows > 0) {
 				echo "error";
 				exit;
 			}
 		} else {
 			$sql = "INSERT INTO users(first_name, last_name, email, password, user_birthday, user_sex) VALUES ('$first_name', '$last_name', '$email', '$password', '$dob', '$user_sex')";
 
 			if($conn->query($sql)===TRUE) {
 				$_SESSION['registeredSuccessfully'] = true;
 				echo "ok";
 				exit;
 			} else {
 				echo "error";
 				exit;
 			}
 		}
 	}
 
 }
 
 ?>