PHP code not working

Hi,

We included a PHP code in one of the slots.
We checked the “Process PHP” option and our code looks something like this:

<?php if ($i==1) { ?>

<div>Ad 1 code</div>

<?php } else { ?>

<div>Ad 2 code</div>

<?php } ?>

But no ad is printed on the screen (everything else works fine) – any idea why?

Thanks

https://ww.wp.xz.cn/plugins/ad-inserter/