I will not charge for the project till it is successfully done as per ypur requirement, I need to check the website and fucntionality of the website to tell you the exact quote and timeline as many freelancers already worked on your project so need to review the code as well.
With expertise in payment gateway integration, customization of payment gateway, API integration, shipping method, PHP, and other technologies, I will like to work on your project.
Kindly share the details so that I can start the work and let you know the solution.
Thanks