Passing and saving a parameter via URL

Hi Everyone –

Im trying to pass a parameter via URL (e.g. /page?myvar=123) and use it on any subsequent page, e.g. three pages later.

I followed advice here, but it doesn’t seem to be working: https://www.webopius.com/content/137/using-custom-url-parameters-in-wordpress

I have the plugin installed containing this code:

<?php
/* Plugin Name: Parameter
Plugin URI: https://webopius.com/
Description: A plugin to allow parameters to be passed in the URL and recognized by WordPress
Author: Adam Boyse and Pete Indelicato
Version: 1.1
Author URI: https://www.webopius.com/
*/
add_filter('query_vars', 'parameter_queryvars' );
function parameter_queryvars( $qvars )
{
$qvars[] = ' myvar';
return $qvars;
}
?>

I have a button on PAGE A that navigates to : /pete-test-pmp-plan-picker?myvar=25

And on the page I want to retrieve the variable, I have this (using an insert php plugin):

[insert_php]
echo hello;
global $wp_query;
if (isset($wp_query->query_vars['myvar']))
{
print $wp_query->query_vars['myvar'];
}
[/insert_php]

On that page I see the “hello” but I don’t see anything about “myvar”.

Please help?!