Common GST Filing Mistakes That Trigger Notices

Most GST notices aren't triggered by deliberate evasion — they come from mismatches that a business could have caught before filing. Here are the ones we see most often in practice.

GSTR-1 vs GSTR-3B Mismatch

If the outward supply figures in your GSTR-1 don't match the summary values reported in GSTR-3B, the system auto-flags the discrepancy. This usually happens when invoices are amended after GSTR-1 is filed but the correction isn't carried through to GSTR-3B in the same period.

Claiming ITC Without GSTR-2B Support

Input tax credit can only be claimed to the extent it appears in your auto-populated GSTR-2B. Claiming credit for an invoice your supplier hasn't uploaded — even if you genuinely paid for the purchase — invites a mismatch notice and potential reversal with interest.

Wrong HSN/SAC Codes

Using an incorrect HSN (goods) or SAC (services) code can misclassify your supply into the wrong tax slab, understating or overstating liability. Businesses above ₹5 crore turnover must report a 6-digit HSN code — a common oversight is continuing to use the 4-digit code after crossing the threshold.

E-Way Bill and E-Invoice Gaps

For businesses above the e-invoicing threshold, an invoice raised without a corresponding IRN (Invoice Reference Number) is technically not a valid tax invoice — this is one of the most common reasons ITC gets denied to the buyer, even though the seller thinks the invoice was properly issued.

A monthly reconciliation between your books, GSTR-1, GSTR-2B, and GSTR-3B before filing catches nearly all of these before they become a notice.