Create a PayPal button using the paypa api.

This should be an easy job for the right coder. I have an existing php solution that does invoicing for me and a programmer who is in charge of it. The problem is that he's not familiar with paypal and I'd like each emailed invoice to include a paypal button so the customer can pay using paypal or their credit card. So, I need someone to basically lay out what needs to be done to add this button to the invoice layout so my current coder can add it in without much effort. I will need some actual code from you so all he needs to do is direct to the correct fields (for amount, item, etc) tied to the paypal button. Good luck bidding!