How to integrate a Payment Gateway into a Website?

Nowadays integrating a payment gateway is very easy. you just need to copy and paste the code they provide you onto your website/app. I recommend you to use IndiaOnlinePay. They have a very low TDR rate and setting up the account is very easy. you just need to fill the sign-up form and their KYC person will contact you within 2-4 hours for documentations.