Finish setting up CGI script /paypal

Hello: This should be a quick project for some one who knows cgi scripts / paypal........... the script is installed, but not working for some reason......... single purchase paypal button when buyer buys need to check out (working) and be sent an email with link to download product..... complete script was already purchased just need to run through and find whats wrong..... have tons of work and can't spend any more time on this......... have many project in the future.. NEED ASAP PK