A bill of supply is what you issue instead of a tax invoice when you cannot charge GST: as a composition dealer, or when everything you sell is exempt. It looks like an invoice but carries no tax.
A regular GST-registered seller charges GST and issues a tax invoice. A composition dealer pays tax on turnover at a flat rate and may not collect GST from buyers, so it issues a bill of supply. A seller of exempt goods or services also issues one.
This editor never adds tax to a bill of supply and puts the composition declaration in the notes. If you only sell exempt goods and are not a composition dealer, change the note to say the supply is exempt.