Add new Cart and add Payment Gateway (not Wordpress)

My project entails developing a new cart and adding payment gateway to an existing system that is not Wordpress. To complete the project, I am looking for an experienced programmer who is fluent in PHP. I do not have any existing cart scripts that need to be integrated into this project, but I already do have an existing payment gateway ready to be incorporated. The ideal freelancer will have a proven track record of developing similar projects and will be able to complete this project in a timely manner. Please don’t hesitate to contact me with questions or additional information. Thank you in advance! Cart system: https://www.securepay.com.au
Admin section has been made to add and mange the products only the following needs to be added.
1. Add to Cart for products brought in website
2. Check out
3. payment gateway integration
4. google login
5. Add to Cart for & Accept payment for class booking
6.Refund payment while cancel the class