php acting weird in wordpress plugin

[bondigor69]

hello people im using an free wordpress plugin called WP Greetbox.
and in the area that I write my own greeting message I tried to execute some php

<?php 
$test = 'test';
echo $test;
?>

but it dosent work???
when I check the source of the page after I see

<!--?php 
$test = 'test';
echo $test;
?--> 

Can someone help please