GST Invoice Rules Every Small Retailer Should Know

What information must every GST invoice include?

A GST invoice legally needs nine fields, regardless of business size or industry — the invoice isn’t compliant if even one is missing, even when the sale itself is fine.

• Your legal business name, address and GSTIN (GST Identification Number)
• A consecutive invoice number, unique for the financial year
• Invoice date
• Customer’s name and address — plus their GSTIN, if they’re GST-registered
• HSN or SAC (Services Accounting Code) code for each item or service sold
• Description, quantity and unit price of each item
• Taxable value, and the tax rate and amount — split into CGST/SGST (Central/State GST) or IGST (Integrated GST) as applicable
• Place of supply, when it differs from the customer’s billing address
• Signature or digital signature of the supplier (not required for e-invoices carrying a valid IRN)

When does e-invoicing become mandatory?

E-invoicing becomes mandatory once a business crosses a turnover threshold set by the CBIC (Central Board of Indirect Taxes and Customs) — above that threshold, an invoice isn’t legally valid until it carries an Invoice Reference Number (IRN) generated through the government’s Invoice Registration Portal. That threshold has been lowered several times since e-invoicing was introduced, so treat any number you read (including this one) as something to verify on the current GST portal rather than take on faith — rules that were accurate a year ago may not be today.

If e-invoicing applies to you, a bill generated outside the portal’s validation isn’t a legal tax invoice, even if every field on it is correct. This is the single most common way growing retailers accidentally fall out of compliance — they cross the threshold mid-year and keep billing the old way for months before anyone notices.

What mistakes cause GST invoices to get rejected?

The single biggest cause is an HSN/SAC code that doesn’t match what was declared in GSTR-1 — most other rejected claims come down to a short list of repeat offenders, not exotic edge cases.

• HSN/SAC code that doesn’t match what was declared in GSTR-1 — the single biggest cause of input tax credit mismatches
• Round-off amounts that push the tax calculation off by a rupee or two, which some auto-reconciliation tools flag automatically
• Wrong place of supply on an inter-state sale, which silently swaps CGST/SGST for IGST and breaks the buyer’s claim
• Sequential numbering that skips or repeats — even accidentally, from switching billing tools mid-year
• Missing the buyer’s GSTIN on a B2B (business-to-business) sale, which downgrades that invoice to a B2C (business-to-consumer) invoice for reporting purposes

How do you stop these mistakes from happening in the first place?

The fix is not re-entering the same data twice. Most of these mistakes happen because billing lives in one tool, stock in another, and the GST return gets built by a third person stitching both together at month-end — by which point a wrong HSN code from three weeks ago is hard to catch. Storely’s billing generates GST-ready invoices directly from the same catalogue and stock records used everywhere else on the platform, so the HSN code, tax rate and invoice sequence are consistent by construction, not by review.