What you are basically doing, is pre-populating the HTML form in the link itself. It will contain everything you would normally put on a form page, without the <FORM...> tags. The syntax can be very exacting, but it's not rocket-science. You can use the PayPal wizard (link below) for encrypted links, or else use the form box below for unencrypted links. Either way, you copy and paste into your email (or web-page).
Encrypted Text Links:
– Log into your PayPal account.
– Click on the Services tab.
– Click the Request Money wizard.
Unencrypted Text Links:
Step-1: Enter Parameters.
– Fill out the form.
– Click the Make Code button.
Step-2: Test the Link.
Step-3: Copy & Paste.
Step-4: Confirmation Email:
– The member receives your email with the link, clicks & goes to the PayPal.
– After he/she completes the transaction, both of you receive a confirming email from PayPal with the transaction details.
– It's from that “official” email that you pick up the member’s name, address, amount, date of payment, etc.