GST Invoice Checklist: Every Field That Gets You Paid Faster

A surprising share of "late payments" are really invoice problems. A wrong GSTIN, a missing PO reference, or a bad HSN code gives the buyer's accounts team a legitimate reason to park your invoice — and their input tax credit depends on your invoice being right, so they will park it. Getting the document correct the first time is the cheapest collections tactic there is.

Rule 46 of the CGST Rules, 2017 lists what a tax invoice must contain. The core checklist:

• Your name, address and GSTIN.

• A consecutive serial number, unique for the financial year — up to 16 characters, letters and numerals, with hyphen or slash allowed.

• Date of issue.

• The recipient's name, address and GSTIN (for registered B2B buyers).

• HSN code for goods or SAC for services — 4 digits if your aggregate turnover is up to ₹5 crore (mandatory for B2B), 6 digits if above ₹5 crore.

• Description, quantity and unit of goods, or description of services.

• Total value, taxable value after any discount, the tax rate, and CGST/SGST or IGST amounts shown separately.

• Place of supply with the state name for inter-state supplies — this decides whether IGST or CGST+SGST applies.

• Whether tax is payable on reverse charge.

• Signature or digital signature of the supplier or authorised person (not required on e-invoices carrying an IRN).

For B2B (registered buyer), the buyer's GSTIN and correct place of supply are non-negotiable — their input tax credit flows only if your invoice details land correctly in their GSTR-2B via your GSTR-1 filing. For B2C (unregistered buyer), you skip the recipient GSTIN; if the invoice value is ₹50,000 or more, you still need the recipient's name, address, and delivery state. Very large businesses (turnover above ₹500 crore) must also print a dynamic QR code on B2C invoices — most SMBs are outside this.

For services, remember the timing rule: the invoice must be issued within 30 days of supplying the service. Habitually invoicing "at month-end" for work delivered on the 3rd both breaks this rule and donates weeks of DSO for free.

E-invoicing is mandatory for businesses with aggregate annual turnover above ₹5 crore, for B2B supplies and exports. It means reporting each invoice to the government's Invoice Registration Portal (IRP), which returns an IRN and a signed QR code that must appear on the invoice. Without a valid IRN, the invoice is legally not an invoice at all — and your buyer cannot claim credit against it. Note also that larger taxpayers (aggregate turnover of ₹10 crore and above) must report invoices to the IRP within 30 days of the invoice date. If you are under ₹5 crore, e-invoicing does not apply, but your buyers above the threshold will care deeply about their own compliance — expect their teams to be strict about yours.

• Wrong or old buyer GSTIN. Companies move offices and GSTINs change with state. Verify the GSTIN on the GST portal before invoicing a new client — a mismatch blocks their credit and your payment together.

• Missing PO or work-order reference. Not a GST requirement, but many buyers' AP systems cannot process an invoice without one. Ask for the PO number before raising the invoice, not after.

• No due date and no bank details. GST law does not require a due date — the buyer's payment process runs on it. Print an explicit date ("Due: 20 July 2026"), full bank details, and a UPI link or QR.

• HSN/SAC errors. A wrong code creates a GSTR-2B mismatch that lands your invoice in the buyer's "hold" queue at reconciliation time.

• Late GSTR-1 filing. Your invoice reaches the buyer's GSTR-2B only after you file. File by the 11th, every month, or your on-time invoice still shows up late on their side.

• Missing Udyam registration number. Also not a GST field — but printing it beside your GSTIN reminds buyers that the 45-day rules under Section 43B(h) and the MSMED Act apply to you.

Sloppy invoice numbering causes both compliance pain and collection pain. Pick one series format — for example INV/2026-27/001 — and stick to it for the whole financial year. Never reuse or skip numbers arbitrarily; gaps invite questions in assessments, and duplicates can get an invoice rejected by the IRP outright. Reset the series each financial year, keep it strictly sequential, and let your invoicing tool own the counter rather than a human memory. A clean, predictable series also makes follow-up easier: "invoice INV/2026-27/042" is unambiguous in a reminder, in your books, and in the buyer's system — which is exactly what you want when you are asking to be paid.