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](https://cleartax.in/s/gst-return-filing-rule-changes-from-july-2025) 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](https://www.caclubindia.com/articles/no-more-auto-itc-in-gstr3b-from-1st-october-2025-54150.asp). 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 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.
## The pre-submit checklist (refuse to file without these)
For the cleanup window leading into this filing, our [14-day cleanup post](/blog/advance-tax-yesterday-14-days-gstr-1-cleanup-gstr-3b-september) walks the bank-recon + IMS pass + credit-note audit. Email contact@softechinfra.com if you want our portal-fail playbook sent before our call.
Sep 20
GSTR-3B due — original deadline
30 min
Sprint duration if cleanup was done by Sep 18
4
Mistakes triggering 80% of notices in 2025
18%
Late fee + interest cost vs cleanup cost
Portal hang prediction for today (Sep 20): The GSTN portal historically degrades on the 19th and 20th of every month between 10 am and 4 pm IST. Today's load will be worse because (a) it is a Saturday with full-day filer activity, (b) the IMS reconciliation flow is heavier this month due to the GST 2.0 cutover prep, and (c) the rate change effective from Sep 22 means many filers are doing one final pre-cutover reconciliation. File before 9 am or after 9 pm.
## The 4 mistakes that triggered notices in 2025
Mismatch between GSTR-1 and GSTR-3B Table 3.1
From July 2025, Table 3.1 is auto-populated from GSTR-1 and non-editable. If you uploaded GSTR-1 with wrong values and did not correct via GSTR-1A in the same month, GSTR-3B inherits the error. The portal accepts the filing; the notice arrives in 14-21 days. Fix at the GSTR-1A stage, not GSTR-3B.
ITC claimed exceeds GSTR-2B available ITC
Until September 2025, the portal flagged this as a yellow warning. From October 1, it is a hard block — submit fails. Today the warning still applies, but treat it as a block. Reconcile via IMS first, then claim only what flows from GSTR-2B + any explicit reversals.
Credit notes not auto-pulled into Table 3.1
CNs raised in August against pre-August invoices sometimes do not auto-flow if the original invoice was filed in a quarter prior to your current QRMP cycle. Manually verify Table 3.1 against your Tally CN register. The fix is a GSTR-1A entry, then a fresh GSTR-3B preview.
Wrong place-of-supply on inter-state supplies
Table 3.2 (inter-state supplies to unregistered persons, composition, UIN) is also non-editable from July 2025. If your B2C-L invoices have wrong POS state codes, your IGST/CGST split is wrong here. The portal allows submit but the auditor will flag at year-end.
1
Minutes 0-5: Portal login and dashboard check
gst.gov.in > Login > Dashboard. Confirm GSTR-1 for August is filed (it should be, by Sep 11). Confirm IMS accept/reject pass is complete (we did this Sep 19). Open GSTR-3B for August. The system shows you a "System Generated GSTR-3B" — your Tables 3.1, 3.2 auto-populated.
2
Minutes 5-10: Verify Tables 3.1 and 3.2 against Tally GSTR-1
In Tally: Display More Reports > Statutory Reports > GST > GSTR-1 > Final summary. Compare line-by-line: Table 3.1(a) vs Tally B2B + B2CL totals; Table 3.1(b) vs zero-rated; Table 3.2 vs B2CS inter-state breakdown. Discrepancy = GSTR-1A required before submit.
3
Minutes 10-18: Table 4 ITC verification
On the portal, Table 4 shows ITC auto-populated from GSTR-2B (after IMS actions). In Tally, Display More Reports > Statutory Reports > GST > GSTR-3B > Table 4. Compare CGST, SGST, IGST values. Any gap is usually due to (a) IMS rejections you forgot to factor in, (b) credit notes against ITC, or (c) reverse-charge inward supplies that need explicit entry.
4
Minutes 18-22: Compute net liability
Portal shows Table 6 — Tax Payable. Output tax (from Tables 3.1 and 3.2) minus ITC (from Table 4) = net cash liability. Verify the number against your CFO's cash flow forecast. If you have a CFO surprise, stop and re-verify before paying.
5
Minutes 22-27: Pay challan
Click "Create Challan" > pre-fill amount > select payment mode (NEFT/RTGS for above ₹10k, net banking for below). For NEFT, generate the mandate and execute it from your bank's net banking — usually credits to GSTN within 30 minutes. For net banking direct, payment lands instantly.
6
Minutes 27-30: File with EVC, save ARN
Once the challan reflects in your cash ledger, return to GSTR-3B. Click "Proceed to File". OTP to your registered mobile. ARN appears on the success screen. Save it (screenshot, PDF, copy to your CA's Drive folder).
A
Switch to incognito mode + a different network
The GSTN portal session has aggressive caching. A fresh incognito window on a 4G hotspot bypasses both the browser cache and any office-LAN throttling. We have seen the same filing succeed on an iPhone hotspot after 3 failed attempts on office wifi.
B
File via the GSP route
If your Tally is integrated with a GSP (ClearTax, Webtel, IRIS), file directly from Tally — F11 > Statutory > File GSTR-3B via GSP. The GSP route bypasses the public portal and goes through the dedicated B2B API endpoint, which is significantly faster on portal-stress days.
C
Wait for off-peak hours
The portal load curve is predictable: peak 10 am - 4 pm IST, low 8 pm - 6 am IST. If you have until midnight on the deadline, file at 10 pm. If you have until tomorrow morning, file at 6 am.
D
Document portal failures with screenshots
If the portal genuinely stays down through the deadline, screenshot every failed attempt with timestamp visible. ICAI and CBIC have historically extended deadlines (the September 2025 GSTR-3B was extended to October 25 due to Diwali — see [CBIC Notification 17/2025](https://x.com/cbic_india/status/1979744426680541347)). Your screenshots support a representation if needed.
| 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 |
- 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
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, ₹95k-₹2.4 lakh fixed scope. First call is with the engineer who would write your TDL or n8n workflow.
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