Bill makers, create invoice.

Need smoke improvements but a good attempt. Keep going and improve it. I am unable to edit the invoice number. Once select down arrow, it shows the bill saved successfully. I am unable to retrieve the old bill. Create inventory and allow user to select from drop-down for both item and quantity. Add individual tax slab for each line item or add it in the inventory itself. Have a plus or minus sign for user to select the tax just in case.