Tax invoice

A tax invoice records a sale and the GST charged on it: who sold, who bought, what, at what value, under which HSN or SAC, at which rate, and the tax split between CGST and SGST or IGST. For a business customer it is also the document that lets them claim input tax credit.

A missing GSTIN, a wrong place of supply or an unnumbered invoice is the kind of small error that costs your customer their credit — and costs you the customer.