Payment Processing via Payment Gateway

A Payment Gateway is a service that authenticate & process the payment between customer and merchant. 
The payment process is as below:

1) Buyer selects the product, clicks on BUY Button in Desktop/Mobile initiating the payment from the merchant's 
   website where user info is collected.
2) This info is sent to the Payment Gateway / Payment Aggregator.

3) Payment Aggregator collects card info in a secure server and passes this through its Acquiring Bank 
   (Payment aggregator's bank) to the Card networks like VISA, MasterCard, American Express etc.
4) The Card Network checks with the Issuing bank (Customer Bank) whether the transaction can be authenticated or not. 
   If Yes, the 3DS URL is sent to the customer where he fills all the details for Authentication.
   
5) If Authenticated successfully, Consumer a/c or card is debited by the Issuing bank.
6) Issuer bank sends confirmation to the card network.
7) This is further notified to the Acquiring bank and then to the payment aggregator.

8) Payment aggregator now send a confirmation to the Merchant, who further informs the consumer.
9) The consumer also gets notified by his bank (Issuing bank) about the transaction.

Payment Gateway Examples in India are: PAYU, RAZORPAY, CCAVENUE, TRAK N PAY, Citrus Pay, HDFC BANK PAYMENT GATEWAY, PayPal, AmazonPayments, BillDesk etc.