I would like to work for this job. Can you please specify more details like
1) Share url of existing website?
2) in which technology existing website is build (Like Core PHP, or any framework)?
3) Assume website is dynamic and admin panel is creadted for webisite.
4) which payment gateway you want to integrate?
I have good experience in web development. Knowledge of technology PHP, MySql, Jquery, javaascript. Also work for payment gateway like Paypal, Strip, quickpay..
Thanks