GSTR-3B for the August 2025 tax period is due today, September 20. We just filed for 11 clients (₹40 lakh to ₹38 crore turnover band, mix of Tally Prime, Zoho Books, BUSY, and a couple of custom Node billing apps). The portal hung twice between 11 am and 1 pm on the IMS reconciliation flow. Two of the four most-common mistakes that triggered notices on the July cycle showed up again. This post is the 30-minute sprint we run, the workaround for the portal hang, and what to do when credit notes refuse to auto-pull.
The answer in 60 words
Login by 6 am or after 8 pm to dodge the portal load peak. Tables 3.1 and 3.2 are auto-populated and non-editable from July 2025 onwards — verify against your filed GSTR-1 before clicking submit. ITC reconciliation flows from your IMS accepted invoices into Table 4. From October 1 onwards, ITC is no longer auto-populated, you enter it manually. Pay challan, file with EVC.
Why this matters today
This is the second GSTR-3B cycle under the hard-locked Tables 3.1 / 3.2 regime introduced from the July 2025 tax period. The July return was the shakedown month — most CAs we spoke to in early August had at least one client get a portal-rejection on submit because GSTR-1 had values that the GSTR-3B cross-check disagreed with.
The August cycle (this one) is also the last "auto-populate ITC" cycle. From October 1, 2025, GSTR-3B Table 4 (ITC) becomes manual entry — auto-populate goes away per the September CBIC notification cluster. Today's filing is the last one where ITC flows in automatically. Use it as a baseline for what your manual numbers should look like next month.
The 4 mistakes that triggered notices in 2025
The 30-minute sprint (run this between 6-9 am or 9-11 pm)
What to do when the portal hangs
This is the workaround we use when gst.gov.in returns a 504 timeout or hangs on the IMS reconciliation flow.
The credit-note workaround
When credit notes raised in your books do not appear in the auto-populated GSTR-3B Table 3.1, three causes and three fixes.
| Symptom | Root cause | Fix |
|---|---|---|
| CN raised in Aug against July invoice missing from Aug GSTR-3B Table 3.1 | CN was not in your filed GSTR-1 for August | File GSTR-1A with the missed CN, regenerate GSTR-3B preview |
| CN raised in Aug against FY 2024-25 invoice missing | Original invoice not in your e-invoice IRN log; GSTN cannot link | Re-issue CN with explicit reference to the IRN of the original invoice; re-file via GSTR-1A |
| CN raised but recipient GSTIN was wrong; CN auto-rejected | Recipient changed GSTIN since the original invoice | Void the CN, re-issue with current GSTIN, file via GSTR-1A |
| CN amount differs from auto-populated Table 3.1 reduction | Tally has gross CN amount; portal computes per-rate breakdown | Verify rate-wise breakdown in Tally CN voucher; mostly a display issue not a filing issue |
The pre-submit checklist (refuse to file without these)
- GSTR-1 for August filed and acknowledged with ARN
- IMS accept/reject pass complete on or before September 19
- Tables 3.1 and 3.2 auto-populated values match Tally GSTR-1 totals to the rupee
- Table 4 ITC matches GSTR-2B post-IMS actions; reverse-charge entries explicit
- Net liability in Table 6 matches CFO cash flow forecast
- Cash ledger has sufficient balance OR challan is paid and credited
- Credit notes auto-pulled into Table 3.1; any gaps fixed via GSTR-1A first
- EVC OTP arrived on registered mobile
- ARN saved in three places: screenshot, PDF download, CA's Drive folder
- Filing summary shared with CFO and ops manager via Slack / WhatsApp
When NOT to use the 30-minute sprint
Three cases where you need more time. (a) First filing under hard-lock regime. If this is your first GSTR-3B since the July 2025 hard-lock, block 90 minutes — you will discover at least one mismatch that needs a GSTR-1A round-trip. (b) Post-merger or post-restructure GSTIN. Cross-GSTIN ITC transfers, transitional credits, and historical period adjustments need time. Do not sprint. (c) Inverted duty structure refund claims pending. If you have an open refund claim for inverted duty structure, the GSTR-3B inputs need to be tagged for the refund flow. That is a CA's domain, not a sprint.
Real example — Bangalore SaaS exporter, ₹18 Cr turnover
A Bangalore B2B SaaS exporter on Zoho Books with 90% zero-rated outward supplies (US/EU customers, LUT in place). August 2025 GSTR-3B sprint: 22 minutes total. Tables 3.1 and 3.2 auto-populated cleanly because GSTR-1 was filed Sep 9 with no errors. ITC was minimal (mostly AWS bills via Reverse Charge Mechanism). The interesting bit was the RCM entries — Zoho Books computes them but does not auto-push to the portal RCM section. Manual entry, 4 minutes.
The portal hung once during the IMS reconciliation step — switched from office wifi to phone hotspot, completed the IMS pass in 90 seconds, returned to the GSTR-3B flow without losing state. Filed at 10:14 pm on a Friday. Total elapsed time: 24 minutes.
We see this clean-sprint pattern more often when the prep work (GSTR-1 cleanup, IMS pass, bank reconciliation) is done on schedule during the 14-day window. Skip the prep, and the sprint becomes a 90-minute scramble.
For broader context on workflows we build for CA practices, see our n8n workflows for CA firms post which walks the WhatsApp reminder + portal-status check pipeline.
Where to read more
FAQ
What if I miss the September 20 deadline?
Late fee at ₹50 per day (₹25 CGST + ₹25 SGST), capped at ₹5,000 per return. Plus 18% per annum interest on the net cash liability from day 1. The Diwali extension to October 25 was announced October 18 — at filing time on September 20, plan for the original deadline.
Are Tables 3.1 and 3.2 truly non-editable now?
Yes, from the July 2025 tax period. The auto-populated values from your GSTR-1/1A flow in and you cannot override at the GSTR-3B stage. The only fix path is GSTR-1A in the same tax period before filing GSTR-3B.
What happens to my ITC if I miss the IMS accept/reject?
If you take no action on a supplier invoice in IMS, it is "deemed accepted" and flows into your GSTR-2B. If you intended to reject it (wrong GSTIN, wrong amount), you have now claimed wrong ITC — fix in next month's IMS by triggering an amendment from the supplier.
Can I file GSTR-3B without filing GSTR-1 first?
Technically yes (GSTR-3B is a self-assessment return), but the portal flags it and your buyer's GSTR-2B will not reflect your outward supplies until GSTR-1 is filed. Practically, file GSTR-1 first, then GSTR-3B.
What is the GSP route for filing?
A GST Suvidha Provider (GSP) is an authorised intermediary that connects to the GSTN B2B API directly. Tally users typically use ClearTax, Webtel, or IRIS as their GSP. The GSP route is much faster than the public portal on stress days.
How does the September 22 GST 2.0 cutover affect my August GSTR-3B?
It does not. Your August GSTR-3B covers transactions dated August 1-31, all under the pre-cutover rate structure. The new rates apply only to transactions dated September 22 onwards, which will appear in your September 2025 GSTR-3B (due October 20, later extended to October 25).
Can I file GSTR-3B from my mobile phone?
Yes. The GSTN portal is mobile-responsive, and the EVC flow uses your registered mobile for OTP. We have filed several GSTR-3Bs from a phone hotspot with the portal in mobile Safari when office wifi was throttled. Speed is identical to desktop on a good connection.
Want a GSTR-3B sprint workflow built for your CA practice?
We build the IMS pass automation, GSTR-1 vs Tally diff alerts, and portal-fail fallback playbook directly into your CA practice management tool — for CA firms managing 25 to 200 clients. Typical engagement: 12 working days, fixed scope. First call is with the engineer who would write your TDL or n8n workflow.
Book a CA Workflow CallFor the cleanup window leading into this filing, our 14-day cleanup post walks the bank-recon + IMS pass + credit-note audit. Email contact@softechinfra.com if you want our portal-fail playbook sent before our call.
