GST E-Invoicing in India — Applicability + IRP Mechanics + Common Errors

What e-invoicing is (and what it isn’t)

When the term “e-invoicing” was first introduced, many businesses incorrectly assumed the Government was launching a centralised portal where everyone had to manually type and generate their invoices.

This is a misconception. E-invoicing does not mean generating your invoice on a Government portal.

Under the GST e-invoicing framework, you continue to generate invoices in your own accounting software (Tally, Zoho, SAP, Oracle) exactly as you always have. The difference is that before you print or email that invoice to your buyer, your software must electronically transmit the invoice data (in a standardised JSON format) to a Government-authorised Invoice Registration Portal (IRP).

The IRP registers the invoice, generates a unique 64-character Invoice Reference Number (IRN), and embeds it into a digitally-signed QR code. This IRN and QR code must be printed on the final invoice you hand to the buyer. E-invoicing is essentially a real-time authentication mechanism designed to eliminate fake invoicing and automate return filing.

Applicability — the turnover threshold timeline

E-invoicing was rolled out in phases to allow the IT infrastructure and business community time to adapt. To determine if you are in scope for FY 2025-26, calculate your “aggregate pan-India turnover” (taxable + exempt + export supplies under the same PAN) for any preceding financial year from 2017-18 onwards.

If your turnover crossed the threshold in any of those years, e-invoicing becomes permanently mandatory for you.

Rollout phase	Effective date	Applicable aggregate turnover threshold
Phase 1	1 October 2020	> ₹500 crore
Phase 2	1 January 2021	> ₹100 crore
Phase 3	1 April 2021	> ₹50 crore
Phase 4	1 April 2022	> ₹20 crore
Phase 5	1 October 2022	> ₹10 crore
Phase 6	1 August 2023	> ₹5 crore (current threshold)

Note: while the GST Council has historically debated lowering the threshold to ₹1 crore, as of the start of FY 2025-26 the ₹5 crore threshold remains the operational baseline. Always verify the latest CBIC notifications.

Who is exempt (regardless of turnover)

Even if a business crosses the ₹5 crore threshold, the Government has exempted specific sectors from generating e-invoices due to high B2C volume or existing regulatory oversight:

1. Special Economic Zone (SEZ) units (SEZ developers are NOT exempt; only SEZ units).
2. Financial sector: banks, financial institutions, NBFCs.
3. Insurance companies.
4. Goods Transport Agencies (GTAs): providing road-transport services for goods.
5. Passenger transportation services: airlines, railways, bus operators.
6. Multiplex cinemas: supplying services by way of admission to the exhibition of cinematograph films in multiplex screens.
7. Government departments + local authorities.

Which transactions need e-invoicing

If your business is in scope, you do not need to generate an IRN for every single transaction. The mandate is targeted at tracking input tax credit flows.

Transactions REQUIRING an e-invoice:

• B2B supplies: sales to another GST-registered person.
• Exports: both with payment of IGST and under Letter of Undertaking (LUT).
• SEZ supplies: supplies to SEZ units or developers.
• Deemed exports (e.g., supplies to Advance Authorisation holders).
• Debit and credit notes: issued against any of the above transactions.
• Forward-RCM: invoices where the supplier is in scope and issuing an invoice where reverse charge applies under Section 9(3).

Transactions NOT requiring an e-invoice:

• B2C supplies: sales to unregistered consumers.
• Exempt supplies: where a Bill of Supply is issued instead of a tax invoice.
• Imports: import of goods (Bills of Entry).
• Self-invoices for RCM: issued under Section 31(3)(f) when procuring from an unregistered supplier.
• Delivery challans / job-work challans.
• ISD invoices: issued by an Input Service Distributor.

For the broader registration thresholds that trigger GST compliance in the first place, see the GST overview pillar.

The technical flow — IRP, IRN, QR code in 6 steps

The operational mechanics of e-invoicing rely on seamless API integration. The lifecycle of an e-invoice:

1. Creation: the supplier generates a normal invoice in their ERP / accounting software. The software converts the invoice details into a standardised JSON payload prescribed by the GSTN.
2. Transmission: the JSON payload is pushed to an authorised Invoice Registration Portal (IRP).
3. Validation: the IRP checks the JSON for syntax errors, ensures the supplier GSTIN is valid, and verifies that the same invoice number hasn’t been used in the current financial year (de-duplication check).
4. IRN + QR generation: on successful validation, the IRP generates a 64-character hash — the Invoice Reference Number (IRN) — and a digitally-signed QR code containing the core invoice parameters.
5. Return + printing: the IRP returns the signed JSON to the supplier’s software. The software then prints the QR code (and optionally the IRN string) on the physical or PDF invoice issued to the buyer.
6. Auto-population: the IRP automatically pushes the registered invoice data to the GST portal (auto-populating the supplier’s GSTR-1 and the buyer’s GSTR-2B) and to the e-way bill portal (generating Part-A of the e-way bill if requested).

The 6 authorised IRPs and how to choose

Initially, the National Informatics Centre (NIC) operated the sole e-invoicing portal (einvoice1.gst.gov.in). To prevent systemic bottlenecks during month-end spikes, the GSTN has authorised multiple private-sector multi-IRP portals:

• einvoice1.gst.gov.in (NIC — primary)
• einvoice2.gst.gov.in
• einvoice3.gst.gov.in (and onwards, managed by private GST Suvidha Providers)

Which should you use? You can route your invoices through any authorised IRP. The IRNs are cross-validated across the entire network in real-time. Most modern ERPs will automatically fail over to a backup IRP if the primary experiences downtime.

Reporting cut-off — the X-day window

Historically, businesses could generate an e-invoice days or weeks after creating the invoice in their books. To enforce real-time reporting, the GSTN introduced strict reporting windows.

• For taxpayers > ₹100 crore: the GSTN implemented a 30-day reporting window (revised from an earlier 7-day proposal). An invoice dated 1 April cannot be submitted to the IRP for IRN generation after 30 April.
• Implementation note for FY 2025-26: the GSTN frequently issues advisories adjusting this reporting window and expanding its applicability to lower turnover brackets (e.g., the ₹50 crore to ₹100 crore bracket). Verify the current reporting cut-off on the GST portal advisory board.

If you miss the reporting window, the IRP will reject the JSON payload. You will be unable to generate a valid e-invoice, rendering the transaction legally non-compliant.

Common operational errors + how to fix them

Finance teams and billing clerks frequently encounter IRP rejections:

1. “Duplicate IRN”: you are trying to generate an IRN for an invoice number that has already been registered in the current financial year. Ensure your ERP’s document numbering sequence is unique.
2. “Invalid GSTIN”: the recipient’s GSTIN is inactive, cancelled, or typed incorrectly. Verify the buyer’s GSTIN on the GST portal before pushing the payload.
3. “HSN code mismatch”: the HSN code provided does not match the GST rate applied. E-invoicing enforces strict validation between HSN codes and tax rates. Use the correct 6-digit or 8-digit HSN based on your turnover. (See GST rates explained.)
4. “State code mismatch”: the Place of Supply (POS) state code does not match the buyer’s registered state (for intra-state B2B), or IGST was applied when CGST/SGST should have been used.
5. “Negative line items”: the IRP does not accept negative values in a standard tax invoice. If you need to reverse a charge or handle a return, issue a credit note and link it to the original invoice.
6. “RCM marker missing”: if you are supplying a notified service under Section 9(3) (GTA, legal services), your JSON payload must explicitly flag the reverse charge parameter as “Y”. (See Reverse Charge Mechanism.)
7. Physical printing error: generating the IRN in the backend but failing to physically print the QR code on the PDF sent to the buyer. A tax invoice without a visible QR code is treated as invalid during transit checks.

IRN cancellation rules — 24-hour window

Mistakes happen. If you generate an IRN for an invoice with incorrect amounts or details, you cannot “amend” the e-invoice on the IRP.

• Within 24 hours: you can cancel the IRN on the IRP portal, provided an active e-way bill has not been attached. (If an e-way bill exists, cancel the e-way bill first, then cancel the IRN.)
• After 24 hours: the IRP database locks the IRN. You can no longer cancel it. The only legal remedy is to issue a formal credit note against that invoice, push the credit note to the IRP to generate a new IRN, and account for the reversal in your GSTR-1.

Integration options — API vs GSP vs ERP vs bulk upload

How you interact with the IRP depends on invoice volume and IT infrastructure:

1. ERP / accounting software (recommended): if you use Tally Prime, Zoho Books, SAP, or QuickBooks, e-invoicing is built in. The software handles JSON conversion, API handshake, and QR code embedding invisibly in the background.
2. Direct API integration: large enterprises with proprietary billing systems can request direct API access to the IRP to build their own custom communication bridge.
3. GSP (GST Suvidha Provider): use a third-party intermediary (Cleartax, Cygnet, etc.) that acts as a secure pipe between your ERP and the IRP, often providing better error-handling dashboards.
4. Offline Excel utility (GePP): for micro-entities with very low B2B invoice volumes, NIC provides a free Excel-based “GST e-Invoice Preparing and Printing” tool. Enter the data in Excel, generate a JSON file, manually upload it to the IRP portal.

What happens if you’re applicable but not compliant

If your aggregate turnover exceeds ₹5 crore and you fail to issue an e-invoice for a B2B transaction, the consequences are severe for both you and your client:

• For the supplier: under Section 122(1)(ii) of the CGST Act, failing to issue a valid invoice attracts a penalty of ₹10,000 or the amount of tax evaded, whichever is higher — per invoice.
• For the buyer: under Rule 48(5), an invoice that requires an IRN but does not have one is not treated as a valid tax invoice. The buyer is legally barred from claiming Input Tax Credit (ITC) under Section 16. (See GST ITC rules.)

In B2B commerce, the commercial pain of your buyer losing ITC is far more damaging than the statutory penalty. Large corporate buyers actively freeze payments to vendors who fail to provide valid e-invoices.

For execution support, see the GST Return Filing service.