Paypal integration in php5.6.4 with very old oscommerce

I am looking to hire a developer to Update PayPal paiement method with the RESTAPI into an old version of osCommerce. The project requires working with PHP, specifically version 5.6.4, to ensure that compatibility with other aspects of the osCommerce websites is maintained. The integration should be completely foolproof, to ensure that all necessary security is in place and minimize any risks of the site being exposed to hackers.

The current system for paypal paiement use the old HTML intégration. Fot security reason we must change that.