NOTE : This uses PayPal PayPal Payments PRO , which is a PAID service. However, all of the validation can be extracted and used on other payment forms to verify the fields. Lastly, a SSL certification should be used when implementing this on a site. The script includes: Validation of all fields Validation of proper credit card lengths / numbers Custom errors Seamless PayPal API integration that sends money without showing PayPals site or having your data in the source code Properly commented and easy to follow code