If you're a practicing CA handling 30-50 GST clients, here's the question that should keep you up at night: what happens when Table 4 of GSTR-3B gets hard-locked?
Outward liability in GSTR-3B is already non-editable since July 2025. The GSTN advisory dated 7th June 2025 made that permanent. No more "Proceed Anyway" buttons. No manual adjustments. If your GSTR-1 data doesn't match, the portal simply blocks you.
Now, with the IMS (Invoice Management System) fully operational and the new "Rejected Records" tab rolled out on 18th February 2026, the direction is clear - ITC hard-locking is next. When it arrives, every mismatch between your purchase register and GSTR-2B will become a locked-in error you cannot fix inside GSTR-3B.
The old workflow of downloading GSTR-2B on the 14th, opening Excel, running VLOOKUP against your Tally/Busy export, and manually fixing mismatches by the 20th is dying. Not because it's slow (it is), but because the system will no longer let you fix things downstream.
This article is a practical guide to surviving and thriving — in this new reality.
Why Your Current Reconciliation Process Is Broken
Let me describe what I've seen watching CAs reconcile across dozens of firms:
Step 1: Download GSTR-2B JSON from the portal on the 14th.
Step 2: Export purchase register from Tally, Busy, or Zoho into Excel.
Step 3: Open both files side by side. Run VLOOKUP on invoice numbers.
Step 4: Manually scan through 500-5,000 rows looking for mismatches - wrong amounts, missing invoices, GSTIN typos, reversed credit/debit notes.
Step 5: Call suppliers whose invoices are missing. Chase them to upload GSTR-1 before the 11th next month.
Step 6: Adjust GSTR-3B figures manually to reflect what you actually want to claim.
Step 7: File on the 20th. Hope nothing breaks.
This worked barely when GSTR-3B was editable. You could fudge the numbers, make manual adjustments, and sort out the differences later. That flexibility was your safety net.
That safety net is now gone.
With hard-locking, what flows into GSTR-3B from GSTR-1 and GSTR-2B is final. If your supplier uploaded an invoice for ₹10,00,000 instead of ₹10,000 and you didn't catch it in IMS before 2B generation — congratulations, your client's ITC is now inflated by ₹9,90,000 and the portal has locked it in.
The fix? You have to catch these mismatches before they enter GSTR-3B. Not after. Before.
The 7-Step Pre-Filing Reconciliation Checklist
Here's the workflow I recommend for every CA handling GST returns in the hard-locking era. It's designed to catch problems early, not fix them late.
Step 1: Reconcile Purchase Register vs GSTR-2B (By the 15th)
The day GSTR-2B generates, match it against your client's purchase register. Not manually — the volume makes manual matching unreliable at scale.
What you're looking for:
- Invoices in 2B but not in your books — the supplier filed something your client hasn't recorded. Could be a genuine purchase the client forgot to book, or could be a fraudulent invoice. Either way, if IMS auto-accepts it (remember: inaction = acceptance in 2026), it enters your 2B and your locked 3B.
- Invoices in your books but not in 2B — the supplier hasn't filed their GSTR-1 yet. Your client recorded the purchase but the credit isn't available. Under hard-locking, you cannot claim this ITC by manually editing 3B. You must either get the supplier to file, or defer the claim.
- Amount mismatches — invoice exists in both but the amounts don't match. Common causes: rounding differences, partial payments recorded as full invoices, or the supplier applied a different GST rate.
- GSTIN mismatches — your client recorded a slightly wrong GSTIN (one digit off), so the VLOOKUP fails even though the invoice exists.
Step 2: Take Action on IMS (By the 16th)
With IMS, every invoice your supplier uploads in their GSTR-1 appears in your IMS dashboard. You can Accept, Reject, or Pend each one.
Critical rule for 2026: Inaction is acceptance. If you don't actively reject a wrong invoice in IMS, the system deems it accepted and it flows into your GSTR-2B.
Go through every invoice in IMS that doesn't match your books and explicitly Reject or Pend it. Don't leave it unattended.
Pay special attention to credit notes — the new "Rejected Records" tab (launched February 2026) now shows rejected credit notes and debit notes separately. If a credit note is rejected by you as recipient, the supplier's output liability gets added back. Make sure your rejections are intentional.
Step 3: Validate RCM and Import of Services (Manual Entries)
Here's a catch most CAs miss: Table 3.1(d) of GSTR-3B — inward supplies liable to reverse charge — is NOT fully auto-populated from GSTR-2B. Import of services under RCM doesn't appear in 2B at all.
Even after hard-locking of the outward liability side, you must still manually ensure:
- All RCM purchases from unregistered suppliers are captured
- Import of services entries are correctly reported
- Self-assessed output tax under RCM matches the corresponding input credit claim
If you miss the output side (Table 3.1d) but claim the input side (Table 4), you'll trigger a mismatch that Rule 88C will flag — and that means an automated notice from the portal.
Step 4: Run Sense Checks on Your Data
Before filing, run these five checks on the reconciled data:
Check 1 - Effective ITC Percentage: Calculate total ITC claimed as a percentage of total purchases. If it's above 18-20% for a trading business, something is wrong — possibly duplicate claims or wrong categorisation.
Check 2 - Duplicate Invoice Detection: Same GSTIN + same invoice number + same amount appearing twice in your purchase register. This is the #1 cause of inflated ITC claims and the first thing an audit will catch.
Check 3 - Zero-Rated Purchases with ITC: If your client has imported goods under zero-rating but is claiming ITC, verify the Bill of Entry details match. With IMS now showing import of goods data (enabled October 2025), cross-verification is possible.
Check 4 - Large Single-Transaction Claims: Any single invoice claiming more than ₹10 lakh in ITC deserves a second look. Verify the underlying invoice exists and the supplier's GSTR-1 matches.
Check 5 - Supplier Compliance Check: Are your top 20 suppliers (by ITC value) filing their returns on time? If a supplier consistently files late, your ITC claim is at risk every month. Identify these vendors and flag them to your client for follow-up or payment withholding.
Step 5: Reconcile Against Previous Period Carry-Forwards
If your client had invoices in last month's books that weren't in last month's 2B (because the supplier filed late), check whether they've now appeared in this month's 2B. These carry-forward credits need to be tracked — otherwise you're either double-claiming or forgetting to claim legitimate ITC.
Many CAs track this in a separate Excel sheet. As the number of clients grows, this becomes a spreadsheet management nightmare.
Step 6: File GSTR-1A If Corrections Needed (Before 3B)
GSTR-1A is your only correction window for outward supplies in the same tax period. It can only be filed once. So if you or your client's sales data has errors in GSTR-1, fix them through 1A before touching 3B.
Once 1A is filed, the updated values flow into the pre-filled 3B. Verify them before filing.
Step 7: Final Cross-Check and File
Compare the pre-filled GSTR-3B against your working paper. The auto-populated figures should now match your reconciled data. If they don't, go back to Step 1 — something was missed.
Only then, file.
The Scale Problem: Why This Breaks at 20+ Clients
The checklist above works for 5 clients. Maybe 10 if you have a dedicated team. But if you're a mid-size practice handling 30, 50, or 100 GST clients each with different ERPs, different export formats, different supplier bases - the manual approach collapses.
Here's the math: 7 steps × 30 clients × 12 months = 2,520 reconciliation cycles per year. At even 2 hours each, that's 5,040 hours — almost 3 full-time employees doing nothing but GST reconciliation.
And that's before you factor in the back-and-forth with clients who send you wrong files, suppliers who don't file, and the portal throwing errors at 11:59 PM on the 20th.
What's Coming Next in GST Compliance
Based on the trajectory of GSTN's advisories and the GST Council's direction, here's what CAs should prepare for:
Table 4 ITC Hard-Locking: Expected to follow the same pattern as outward liability — auto-populated ITC values from GSTR-2B will become non-editable. When this happens, every mismatch in your 2B reconciliation becomes a locked-in error. The only fix will be through IMS (accept/reject before 2B generation) or carry-forward to the next period.
Mandatory IMS Adoption: IMS is currently optional but the hard-locking of GSTR-3B makes it practically mandatory. If you're not using IMS to manage inward invoices, you're accepting whatever your suppliers upload - errors and all.
GST 2.0 Rate Rationalisation: The GoM has recommended moving from 4 slabs to 2 (5% merit + 18% standard). When rates change, every outstanding invoice at the old rate needs special handling. This is a reconciliation event that will affect every business in India.
GSTR-9/9C Getting Stricter: Tables 12 and 13 are now mandatory from FY 2024-25 onwards. The annual return requires precise, rule-wise documentation of ITC claimed and reversed. If your monthly reconciliation is sloppy, the annual return will expose every gap.
The Bottom Line
The GSTR-3B hard-locking era is not a minor compliance tweak. It's a fundamental shift from "fix it later" to "get it right the first time." The portal will not let you adjust anymore. The IMS will not wait for you to review invoices.
As a CA, your value to clients is no longer just filing returns on time - it's ensuring the data is clean before it enters the system. That means better reconciliation, faster supplier follow-up, and smarter tooling.
The spreadsheet era of GST compliance is ending. The question is whether you're ready for what comes next.
The author is a Computer Science student at the University of Manchester and the founder of MatchaNow, a privacy-first tax reconciliation platform. He previously built a GenAI platform at AWS that was adopted by Emirates, BT, and Capgemini, and showcased at AWS re:Invent 2025. MatchaNow is free to use at matchanow.org .
The views expressed above are the author's own. Readers are advised to consult a qualified tax professional for specific compliance matters.
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