Opencart Paypal Payment Gateway Modification

General information for the website: Create Paypal Payment Gateway API Modification for Opencart
Kind of development: Customization of existing website
Description of every page/module: For Opencart 1.5.6.4 + 2.2
Modify all Paypal payment methods (Standard, Express, Mail etc) in Opencart to manipulate the payment processor into believing the payment is coming from another website.

E.g.
I have a real store ABC.com and a fake store XYZ.com . Both use Opencart. You are going to create a payment gateway API.
Then when customers buy at the real store ABC.com, they will be redirected to the payment gateway at XYZ.com and make payment at paypal. So once paid, Paypal will send the notification to XYZ.com which will then update the order status at the real store ABC.com

Paypal must always think the payment is coming from XYZ.com (fake store) and not ABC.com (real store).

STORE => GATEWAY => PAYPAL
IP store => IP gateway => Paypal

Create an API to receive the payments from the opencart store and all credentials related to paypal will be registered on the new gateway.
Once you click confirm order on store the customer will go the gateway, and from there redirected to paypal. When paypal notifies it will notify the gateway e the gateway will basically get the transaction ID see to what store its related to and send a callback to that store to update the order.


Opencart Payment Modules:
1. PayPal by Email
2. PayPal Express Checkout
3. PayPal Payments Standard
4. The rest of the Paypal modules
Description of requirements/features: Experience in Opencart, Paypal and Payment Gateway APIs.
Payment methods: Credit Card, Paypal
Extra notes: