Help me fix a Paypal IPN script!

I've created a website with a purchasing facility. This facility basically enables the user to click a "Buy Now" button to pay by Paypal. The script parses three key variables to Paypal: **item_name (string) item_number (integer) price ** Paypal then does the usual IPN stuff. I have used a template for the **[login to view URL]** file from the following site: [login to view URL] Although my code looks fine and Paypal receives payments successfully (I am using Paypal sandbox), my **[login to view URL]** file returns an "Invalid IPN" message by e-mail and my database does not update the order to show that payment has been made. If you look at the sample [login to view URL] file from the above website, there are three main bits - if, else, else if - it seems the script is not parsing the first "if", and is going to the "else if", which is the "Invalid IPN" bit. I just need someone to help me get this working. Hopefully it's quite straight forward - I'm guessing a lot of you will have done the same thing before. If you want to use a pre-tested script you've already written before and simply adapt it for my website, that should be fine. I'd like someone to start working **immediately** as I need this done ASAP. I'd like you to communicate with me via MSN Messenger using good English. Thanks for your time Adam