Intergration with PayPal in PHP environment - Installment Plan

Required: Intergration with PayPal in PHP environment, which includes an option for the customer to set up an installment plan through PayPal. All the files for a complete PayPal flow are required. ## Deliverables The uploaded zip file contains the invoice sample page. Requirements: 1. All the code to provide a complete PayPal flow from creation of installment plan ( or a single payment) to payment notifications through IPN. 2. Extensive error checking. 3. Installment plan code should support from 2 to 5 installments. 4. Dates of installment payments may be NOT at regular intervals ( variable payment dates). 5. Each installment has its UID that should be also returned by payment notification. 6. We should be able to test the flow in the PayPal sandbox. All sandbox ( and in production real PayPal) parameters should be isolated in a separate php include file. 7. All the button generation code must be encrypted.