How to File GSTR-1: Step-by-Step Guide for E-commerce Sellers (FY 2026-27)

Your GSTR-1 affects more than just your own filing. Every invoice you declare in GSTR-1 flows into your buyer's GSTR-2B — the statement they use to claim input tax credit. File late or file wrong, and your B2B customers lose ITC they were counting on. That's the kind of compliance failure that ends supplier relationships.

The deadline is the 11th of every month. Not the 20th — that's GSTR-3B. Two different returns, two different deadlines, one week apart, both mandatory. The 11th is for what you sold. The 20th is for what you owe.

What GSTR-1 Contains — Tables That Matter for Sellers

GSTR-1 has 13 tables. You don't need all of them. As a marketplace seller, these are the ones you'll actually use:

Table	What Goes Here	When You Use It
4A	B2B invoices — taxable supplies	Every invoice issued to a GSTIN holder
4B	B2B reverse charge supplies	If your buyer pays GST instead of you
5	B2C large invoices (above ₹2.5L interstate)	High-value direct sales to unregistered buyers
7	B2C small invoices (all other B2C)	Bulk retail sales — summarised, not invoice-by-invoice
9A	Amendments to B2B invoices	Correcting a previously filed B2B invoice
9C	Amendments to B2C small	Correcting a previously filed B2C summary
11	Advances received / adjusted	Only if you raise advance invoices
12	HSN Summary	Mandatory for all filers — 4-digit or 8-digit HSN

E-commerce sellers selling to end consumers almost entirely use Tables 7 (B2C summary) and 12 (HSN). Sellers with wholesale B2B buyers use Table 4A extensively. A seller on Flipkart who also supplies to kirana stores offline uses both.

The 2026 HSN Change — Read This Before You Open the Portal

From FY 2026-27, the GST portal enforces HSN codes at the point of entry. This is the single biggest GSTR-1 pain point in 2026.

• Turnover above ₹5 crore: Mandatory 8-digit HSN codes
• Turnover ₹1.5 crore to ₹5 crore: Mandatory 4-digit HSN codes
• Turnover below ₹1.5 crore: HSN optional (but strongly recommended)

The portal's HSN validation runs against the official master list. If you type an HSN code that doesn't exist or is discontinued, the table rejects your entry — it won't display an error message, it simply won't accept the input.

Before starting any GSTR-1: Go to gst.gov.in → Services → User Services → Search HSN Code. Verify every product code you sell against the live master list. Do this once, save the list, use it every month.

Rajesh sells phone accessories on Meesho — screen protectors, cases, and cables. He had been using HSN 8473 (parts of computers) for phone accessories since 2021. The 2026 portal update rejected it. The correct code for mobile accessories is 8517 (telephone sets and parts). He discovered this when the portal refused to accept his Table 12 entry in April — on the 10th, one day before the deadline. Correct your HSN codes now, not under deadline pressure.

Step-by-Step: Filing GSTR-1 on the GST Portal

Before you start — prepare these:

• Your sales register or invoice export from your accounting software for the month (April 2026 → file by May 11)
• A reconciled list of invoices: B2B (to GSTIN holders) vs B2C (to consumers)
• HSN codes verified against the portal master list
• Credit and debit notes issued for the period

---

Step 1 — Log in and open Returns Dashboard.

Go to gst.gov.in → Login → enter GSTIN, password, captcha. Navigate: Services → Returns → Returns Dashboard. Select Financial Year: 2026-27 and Tax Period (month or quarter). Click Search.

---

Step 2 — Select GSTR-1 and choose preparation mode.

You'll see the GSTR-1 tile. Click Prepare Online for volumes below ~100 invoices. For higher volumes, use Prepare Offline — download the Excel offline utility from the portal, fill your data, generate a JSON file, and upload it.

The online entry portal times out during peak filing days (10th and 11th of each month). If you have more than 50 invoices, use the offline utility — upload at off-peak hours (before 9 AM or after 10 PM).

---

Step 3 — Fill Table 4A: B2B Invoices.

For every invoice issued to a GST-registered buyer, enter:

• Receiver's GSTIN (15-digit)
• Invoice number, date, invoice value
• Place of supply (state code)
• Whether supply is reverse charge (usually No)
• Taxable value, IGST or CGST+SGST rate and amount

The portal auto-validates the receiver's GSTIN against the GST registration database. An invalid GSTIN causes the entry to fail. Verify buyer GSTINs before entry using the GST portal's GSTIN search.

For marketplace B2B sales: If an Amazon business buyer provides their GSTIN at checkout, that invoice goes in Table 4A. If no GSTIN was provided (which is most consumer purchases), it goes in Table 7.

---

Step 4 — Fill Table 7: B2C Summary.

For all sales to unregistered buyers (most e-commerce retail), you don't enter invoice-by-invoice. You enter a rate-wise summary:

• State of supply (intra-state vs inter-state)
• GST rate (0%, 5%, 12%, 18%, 28%)
• Total taxable value at that rate
• Total tax amount

One row per rate per state. A seller with intra-state Karnataka sales at 12% GST and 18% GST fills two rows. An inter-state seller with buyers in 15 states at 18% GST fills one row (inter-state B2C is consolidated regardless of destination state if invoice value is below ₹2.5L).

---

Step 5 — Fill Table 12: HSN Summary.

Mandatory for all filers. For each HSN code you sold under:

• HSN / SAC code (4-digit or 8-digit as required)
• Description of goods/services
• UQC (Unit Quantity Code — pieces, kg, litres, etc.)
• Total quantity
• Total taxable value
• Integrated tax, central tax, state tax amounts

The portal validates HSN codes in real time. If your code is invalid, the row turns red and won't save. Fix the HSN before proceeding — you cannot file with unresolved table errors.

---

Step 6 — Add credit and debit notes (if any).

Returns, cancellations, and price adjustments are not negative invoices. They go in Tables 9B (credit notes to registered buyers) or Table 10 (credit and debit notes for unregistered buyers).

For marketplace sellers, the most common entry here is a credit note for goods returned by a buyer — where the original invoice was issued and the return happened within the same or following month.

---

Step 7 — Review the GSTR-1 Summary.

Before submitting, click Preview / Generate Summary. Check:

• Total taxable value matches your sales register total
• IGST + CGST + SGST amounts cross-check with your invoice totals
• Table 12 HSN totals match the sum of Tables 4–7 supplies
• No red flags or validation errors on any table

A summary mismatch between your GSTR-1 and your GSTR-3B is one of the primary triggers for a GST scrutiny notice. Reconcile these before filing both returns each month.

---

Step 8 — Submit, then File.

Click Submit GSTR-1. This freezes your data — you cannot edit after submission. Then click File Return.

Choose your authentication method:

• EVC (Electronic Verification Code): OTP to your registered mobile and email — available for sole proprietors and individuals
• DSC (Digital Signature Certificate): Mandatory for companies and LLPs; optional for others

On successful filing, the portal generates an ARN (Acknowledgement Reference Number). Save this — it's your proof of filing and is required for any future amendments or dispute resolution.

---

The Three GSTR-1 Mistakes That Trigger GST Notices

Mistake 1 — Reporting net sales instead of gross. Your GSTR-1 should declare the full invoice value before platform fees, TDS deductions, and returns. The amount your marketplace settles to your bank account is not your sales figure for GST purposes. If your Amazon settlements total ₹40L for the month but gross invoices were ₹48L (before returns and fees), ₹48L goes in GSTR-1.

Mistake 2 — Mismatch between GSTR-1 and GSTR-3B. Your tax liability in GSTR-3B must match the outward supply tax declared in GSTR-1. The GST portal cross-validates these automatically. A ₹50,000 gap triggers a system notice — Section 61 scrutiny — within days, not months.

Mistake 3 — Late or missing B2B invoices. A B2B buyer's ITC shows up in their GSTR-2B only after you've filed GSTR-1 with their invoice. If you file 3 days late, their reconciliation for the month shows missing ITC. They'll call you. Possibly their CA will call you. File on time — it's not just your compliance at stake.

QRMP Sellers: The IFF Shortcut

If your turnover is below ₹5 crore and you're on the QRMP scheme, you file GSTR-1 quarterly. But your B2B buyers need their ITC monthly. The IFF (Invoice Furnishing Facility) solves this:

• Upload only B2B invoices for months 1 and 2 of the quarter (no B2C, no HSN summary required in IFF)
• IFF due: 13th of the following month
• Month 3 is covered in the full quarterly GSTR-1 (due 13th after quarter end)

For a seller with mostly B2C sales on Meesho, IFF is optional — your buyers are unregistered consumers with no ITC to claim. For a seller with B2B wholesale customers, IFF is essential.

Full compliance calendar with every GST due date → How to file GSTR-3B after filing GSTR-1 → Get monthly GSTR-1 filing handled by a CA →

The 11th comes around every month without fail. The sellers who have their invoice data ready on the 9th, run the HSN check, and file by the 10th never think about GSTR-1 at all. The ones who start on the 11th morning spend the afternoon fighting a portal that has 2 million other filers trying to do the same thing.