[Plugin: Formidable Forms] How do I mix some PHP code into my Form?

I am using Formidable PRO, bought and paid for ??
So far quite pleased ?? ??

I’ve built a form and defined in its notification options a mail message.

All this works so far.

Now I want to mix into the mail message a value I calculate with PHP code.

Can I mix <?php … ?> into the message text? So far I have not been able to.

If not do I have some alternative?

Thanks