Your code seems Ok, but is your plug-in correctly installed? You have to upload your urp_functions.php in a folder inside the /wp-content/plugins/ folder and in your urp_functions.php file, you have to insert comments so it gets detected as a plugin. here is the example comment on WordPress codex :
<?php
/*
Plugin Name: Magic Plugin
Plugin URI: http://example.com/magic-plugin
Description: Magic Plugin performs magic
Version: 2.3
Author: Mr. Magic
Author URI: http://example.com/
*/
Then once you have done this, you still have to go inside your admin panel and activate the plugin! Have you done all this?