help w/redirect

<?php
$link = mysqli_connect("localhost", "root", "", "prerentdb");
// Check connection
if($link === false){ die("ERROR: Could not connect. " . mysqli_connect_error()); }

$id='id';
echo "<center>";echo date('m/d/y');echo "<br />";

// Attempt select query execution
$result = mysqli_query($link,"SELECT * FROM numbers");
$row= mysqli_fetch_array($result);

$id='id';
$expiry='expiry';
if ($_POST["expiry"] === $_POST["confirm_password"]) {

$sql = "UPDATE numbers SET expiry = $expiry-1 where id=$id  ";
if(mysqli_query($link, $sql)){ echo "expiry was updated successfully."; }
else { echo "ERROR: Could not able to execute $sql. " . mysqli_error($link); }

if ($expiry == 0) // go to expiredpage.html
 {
header("location:expiredpage.html");
 }

else  // go to sysnav.html
  {
header("location:sysnav.html");
 }
// Close connection
mysqli_close($link);
?>

Edited by hamluis, 08 August 2021 - 07:30 PM.
Merged topics - Hamluis.

 

I want to change a duedate up to a month later. I think the below code is what I want if I change it
correctly:
$startDate = '2021-06-03'; // do I leavee as is? Is the date shown just to show format?
$nMonths = 1; // move ahead one month
$final = endCycle($startDate, $nMonths); // I changed "$final" to "$duedate"? this is line 41
I got:
Fatal error: Uncaught Error: Call to undefined function endCycle() :41 Stack trace: #0 {main} thrown