code disappears after saving

Hi,

I’m trying to add php code to the form:
<input type=”hidden” name=”recommend” value=”<?php echo $recommend; ?>” />
but after saving it looks like this:

<input name=”recommend” type=”hidden” value=” &lt ; ?php echo $recommend; ? &gt ;” />
in value instead < and > is &lt ; and &gt ;
and it doesn’t work

Can you tell me how can i fix it??

thanks
Michal

https://www.ads-software.com/plugins/wp-super-popup/