gistfile1.txt

<?php
/*
 Plugin Name: rewrite test
 Description: rewrite test
 Author: Nick
 Version: 1.0
 */
 

register_activation_hook(__FILE__, 'activate');
function activate()
{
    // matches https://www.mycelltracker.com/tracker/8BA21D90-3F90-407F-BAAE-800B04B1F5EB
    add_rewrite_rule('tracker/[0-9a-fA-F]{8}(?:-[0-9a-fA-F]{4}){3}-[0-9a-fA-F]{12}/?', 'index.php?pagename=tracker&t=$matches[1]', 'top');
    //add_rewrite_tag('%tracker%','([^&]+)');
    flush_rewrite_rules();
}

add_filter( 'query_vars', 'my_query_vars' );
function my_query_vars($query_vars)
{
    $query_vars[] = 't';
    return $query_vars;
}

add_filter('template_redirect', 'my_template_redirect');
function my_template_redirect() 
{    
   exit(var_dump(get_query_var('t')));
}
 
 
register_deactivation_hook(__FILE__, 'deactivate');
function deactivate()
{
    flush_rewrite_rules();
}