• How to maintain sale records (book keeping) ecommerce having COD

Hi all,

I want to ask the following questions. Hope I will get satisfactory answers from experienced CAs.

Business background: 
We run an ecommerce business through our own website (no marketplace like flipkart, amazon etc) and sell ayurvedic medicines online. We accept payments through Cash on Delivery mode (we have tie up with blue dart courier for COD), online mode (through Payumoney and EBS payment gateway). 

The orders received online are shipped on the next day. COD remittances are credited to our bank account every 15 days (payments for orders delivered between 1-15 of the month are cleared by the courier company on the 1st of the next month.).

At the end of the month we calculate total number of orders received between date 1-30 and total value of the orders (total sales amount). Now out of this total sale only 20-25% orders are prepaid (online payment mode) while majority of the orders are "cash on delivery mode" whose payments we are yet to receive or partially received on the 1st of the next month. How do we calculate our liability to pay Sales Tax (VAT)? Do we pay VAT on total sales irrespective of whether we have been paid or not for the order?

If we need to pay tax on the total sales amount then what will happen when a customer refuses to accept a COD order? In this case the order is returned back to us and double shipping (to and fro) is charged by the courier company. We are paid nothing for such orders and we have incurred shipping expense on this. In which account this expense will go and what will be the case for VAT since we have already paid VAT on this sale but the sale was cancelled by the customer. Do we get a refund for this VAT? If yes then how?

Thanks in advance.