Sometime, your customer pays double time through payumoney (payment gateway) or sometime, you will not have the stock. At that time, it is very necessary to refund the customer's money. In payumoney, there is option refund. Use it for refunding the money. It will take few hours. Same time, page will show, refund is in processing. After successful refund, it will show refunded. Enjoy with your customer's happiness.