delivery challan

You can adopt any method but there should be these details in your invoice

1. Name, address and GSTIN of the supplier
2. Tax invoice number (it must be generated consecutively and each tax invoice will have a unique number for that financial year)
3. Date of issue
4. If the buyer (recipient) is registered then the name, address and GSTIN of the recipient
5. If the recipient is not registered AND the value is more than Rs. 50,000 then the invoice should carry:
    i. name and address of the recipient, 
   ii. address of delivery, 
   iii. state name and state code 
6. Hsn code or accounting code of services**
7. Descripttion of the goods/services
8. Quantity of goods (number) and unit (metre, kg etc.)
9. Total value of supply of goods/services
10. Taxable value of supply after adjusting any discount 
11. Applicable rate of GST
(Rates of CGST, SGST, IGST, UTGST and cess clearly mentioned)
12. Amount of tax
(With breakup of amounts of CGST, SGST, IGST, UTGST and cess)
13. Place of supply and name of destination state for inter-state sales
14. Delivery address if it is different from the place of supply
15. Whether GST is payable on reverse charge basis
16. Signature of the supplier