A bill or an invoice can be prepared in handwriting but should contain the following details:
- Name of buyer
- GSTN of buyer
- GSTN of seller
- Address of supply, buyer and seller
- Product description with HSN code
- Tax rate and tax charged for each product
A hand written or pre-printed bill is allowed under GST.
However I will suggest to go for a billing software as the details needs to be uploaded on GST portal every month and it will be dual work to make bills and then again put them in excel to upload on GST portal.