I need help with a variable

[Anon]

I am trying to setup a page that my customers can go to fill in the amount that they owe on an invoice then when they press the submit button they are directed to my account at 2checkout.com with the amount they filled in on the opening page. I need the ability to pass the total they fill in as a varible. This works if I hard code this with the code below as a link, but I need my customer to be able to fill in an amount. Can you help me with this? Here is the code that is hard coded to recieve $75.00:
https://www.2checkout.com/cgi-bin/sbuyers/cartpurchase.2c?sid=16076&cart_order_id=001705&total=75.00
Thanks in advance for looking at this post.
Doug

[Anon]

First check to see if the form is being submitted. If it is, then redirect to 2checkout.com with the entered value, and if not, then just print the form:

<?php
if ($submit) {
header("Location: https://www.2checkout.com/cgi-bin/sbuyers/cartpurchase.2c?sid=16076&cart_order_id=001705&total=$user_total");
}
else {
// print the form
}
?>

Be sure to call the form page as the form action.

[Anon]

thanks James