e commerce business for outside india

I have registered under GST. I am selling different types of goods online through my web site all around the world, shipment through DHL . which is under valued means 20 dollar. but through pay pal I am getting 50 dollar which is real. as per customer request showing under valued. in future any problem I am getting more which is showing in DHL shipment receipt. DHL shipment receipt and bank account can reconile. how to do? pls guide us.