HELP: PHP redirect with url parameter on wordpress

Hello all,

Not sure if this should work with wordpress or not (or it may just be my lack of php knowledge). I got it to work on another non-wp site I built easily so I know the code is solid. It must be some sort of conflict with WP right?

Here is how it should work:

When a parameter is added to the url, example: http://www.mysite.com/?id=1234 it then redirects to a specific URL which is defined by "1234" on another website via a custom API.

first line of code on my index.php file is
<?php include 'redirect.php'; ?> which has all the info for the redirect its self.

I was thinking I would put the same line in root/index.php at the top and include redirect.php in the same folder and everything would work but it's not functioning. It's just returning a blank page :-/

Could it be because the wordpress index.php already has to call other wordpress files?

I'm completely lost. :-(

Any help would be greatly appreciated. I would also be willing to pay someone to fix this if required.

Thank you very much for your time.