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I have a registration form at http://mutualpay.byethost7.com/wp/register.php?i=1.. my form action is signup.php..i created the file but it doesnt seem to work at all, when i click the signup button it loads to http://mutualpay.byethost7.com/wp/signup.php?i=2 , its like it is not executing the codes in the file

Here is my signup.php code

<?php session_start(); include 'dpconfig.php';
$first = $_POST['firsts'];
$last = $_POST['last'];
$uid = $_POST['uid'];   
$pwd = $_POST['pwd'];

if (empty($firsts)){
 header("Location: register.php?error=empty");
  exit();
}
if (empty($last)){
 header("Location: register.php?error=empty");
  exit();
}

 if (empty($uid)){
 header("Location: register.php?error=empty");
  exit();
}

if (empty($pwd)){
 header("Location: register.php?error=empty");
  exit();
}
else {
  $sql = "INSERT INTO user (firsts, last, uid, pwd)
 VALUES ('$firsts', '$last', '$uid', '$pwd')";
   $result = $conn->query($sql);
  header("Location: index.php")
}

its like this code are not executed, cos after clicking on the signup button, it brings a blank page, I dont know what can be the cause, any help appreciated.Thanks

In the first empty-check you check an undefined variable ($firsts). I guess you meant $first, but php does not guess like we humans do.

change your code to

if (empty($first)){

edit: you could also merge those 4 empty-checks into one if, in order to have less code and better readability:

if (empty($first) || empty($last) || empty($uid) || empty($pwd)){
    header("Location: register.php?error=empty");
    exit();
}

The problem comes from your host, byet.
Byet uses an "antibot" system, which redirects you with javascript (mostly not executed by bots) to the same location and adding 1 to the i passed argument.
The problem is: the post arguments aren't passed when redirecting which mean that the $_POST var'll be empty.

Also check if isset($_POST['firsts']) and for your passed arguments to the $_POST variable or it might create undefined var errors.