GSTR-1 for August 2025 is due on September 11 — nine days from today. We just finished the August batch for 14 SMB clients (₹40 lakh to ₹38 crore turnover band, all on Tally Prime 5.x or Zoho Books). The same four reconciliation mistakes that triggered notices on the July cycle showed up again in the first six August files. This post is the exact 60-minute Tally-to-portal sprint we run, plus the four mistakes that get the GSTN portal yellow-flag treatment within a week of filing.
The answer in 60 words
Export GSTR-1 JSON from Tally Prime via Display More Reports > Statutory Reports > GST > GSTR-1. Reconcile B2B invoice values against your e-invoice IRN log first — not against the books. Validate Table 12 HSN summary using the new dropdown HSN selector. Upload JSON, fix any portal validation errors, file with EVC. Total time: 60 minutes if you ran the cleanup checklist on September 8.
Why this matters this week
The July 2025 GSTR-1 cycle was the first full month under the hard-locked GSTR-3B Tables 3.1 and 3.2 — your GSTR-1 numbers now flow into GSTR-3B with zero edit room. A wrong invoice value in GSTR-1 is a wrong tax liability in GSTR-3B. The portal has rejected ITC for 12 of our supplier counterparties so far this quarter due to GSTR-1 mismatches that the seller did not catch on day one.
The September 11 due date is not the deadline you should plan for. The real deadline is September 8 — three days before — so you have a 72-hour window to reconcile portal errors without incurring the ₹50/day per return late fee.
The 4 mistakes that triggered notices in 2025
The 60-minute sprint (run this on September 8 or 9)
What actually breaks (real failures from the August batch)
These are the actual portal errors we hit in the August 2025 batch, with the fix that worked.
| Portal error message | Root cause | Fix in Tally |
|---|---|---|
| "Duplicate invoice number for the same financial year" | Same invoice number used in both prefixed and non-prefixed forms | Voucher class > "Restart numbering" set to "Yearly" with explicit prefix INV/2025-26/ |
| "HSN code not found in master" | 8-digit code not present in GSTN dropdown for your turnover band | Truncate to first 6 digits in Stock Item master, regenerate JSON |
| "Place of supply mandatory for B2CL above 2.5 lakh" | Customer ledger has no state populated | Customer master > GST Details > Place of Supply field, set state code |
| "Original invoice not found for credit note" | Credit note references an invoice from a prior period that was never filed in GSTR-1 | Re-issue the credit note referencing the actual filed invoice number |
| "GSTIN of recipient invalid" | Recipient changed GSTIN during the year, Tally still has old one | Update party master, re-export the affected invoices only |
The pre-flight checklist
- IRN log from einvoice1.gst.gov.in matches Tally e-invoice report by count and total value
- Every HSN in Table 12 verified against the GSTN dropdown
- Every credit note has a verified-existing original invoice reference
- Every B2C-L row above ₹2.5 lakh has a state code in place of supply
- Customer GSTINs in party master verified against the Aug e-invoice batch
- Tally invoice numbering is "Restart numbering: Yearly" with prefix INV/2025-26/
- JSON exported, uploaded, "Processed with errors" status investigated and cleared
- Draft preview PDF totals match your Tally GSTR-1 report
- EVC OTP arrived on registered mobile, ARN saved to your file system
- If running close to deadline, GSTR-1A path planned for any post-filing corrections
When NOT to use this 60-minute workflow
Three cases where the sprint is the wrong tool. (a) First time filer, complex business model. If you are filing GSTR-1 for the first time after crossing the ₹40 lakh threshold, the 60-minute sprint assumes a CA has already set up your Tally GST configuration correctly. Pay a CA for the first three filings. Build muscle memory before going DIY. (b) Composition scheme to regular taxpayer transition mid-year. The reconciliation between composition GSTR-4 history and your first regular GSTR-1 is not a 60-minute job. Block half a day. (c) Multi-GSTIN business with inter-branch transfers. If you have GSTINs in three states and inter-branch stock transfers, every transfer is an inter-state outward supply on the source GSTIN. The reconciliation is across at least three Tally companies. Block 4 hours per filing month, or hire a CA who specialises in multi-state.
Real example — Surat textile exporter, ₹14 Cr turnover
A Surat textile exporter on Tally Prime 5.0 with monthly e-invoicing. August 2025 cycle: 1,840 invoices across 11 buyers in the US, UAE, and Bangladesh, plus 240 domestic B2B invoices to job-work converters in Tirupur and Erode. The first sprint attempt missed 38 e-invoices because the IRP API token had expired on August 19 and the integration silently failed. The reconciliation step caught it. We re-ran the e-invoice generation in batch mode (Tally Prime 5.x supports this natively from the GST > Generate IRN screen), pulled them into the GSTR-1 export, and filed clean. Total elapsed time: 90 minutes including the IRN catch-up. Without the reconciliation step, the next month's GSTR-2B mismatch would have delayed ITC for three of those buyers.
We work on similar GST-tied accounting workflows for other clients on our AI automation team — most of the time the work is integration-and-recovery, not greenfield.
Where to read more
FAQ
What is the actual due date for August 2025 GSTR-1?
September 11, 2025. Monthly filers must file by the 11th of the following month. QRMP scheme filers (turnover up to ₹5 Cr) file the August month details in their Q2 (Jul-Sep) return, due October 13, but typically use the IFF facility to upload B2B invoices monthly to keep buyer ITC flowing.
Can I edit GSTR-1 after filing?
No, GSTR-1 itself is non-editable once filed. Use GSTR-1A to make corrections within the same tax period before filing GSTR-3B. Beyond that, amendments go in the next month's GSTR-1 in Tables 9, 10, 11.
What happens if I miss September 11?
Late fee starts at ₹50 per day (₹25 CGST + ₹25 SGST), capped at ₹5,000 per return. More importantly, your buyer's GSTR-2B for August will not include your invoices, and they cannot claim ITC. Expect calls from your buyer's accounts team within a week.
Does Tally Prime auto-validate HSN codes against the GSTN dropdown?
Tally Prime 5.x has an HSN code validation feature for stock items, but the master list updates lag the GSTN dropdown by 4-6 weeks. Always cross-check Table 12 against the live portal dropdown before filing — especially for new SKUs added in the tax period.
Is e-invoicing mandatory for my August 2025 invoices?
If your aggregate annual turnover (AATO) in any year from FY 2017-18 onwards exceeds ₹5 Cr, yes — e-invoicing for B2B invoices is mandatory. The threshold dropped to ₹5 Cr from August 2023. Confirm by checking the latest CBIC notification on cbic-gst.gov.in.
Can I file GSTR-1 from Zoho Books instead of Tally?
Yes. Zoho Books generates GSTN-compliant JSON via Reports > Tax > GSTR-1 > "Push to GSTN". The 60-minute sprint above translates one-to-one — only the menu paths change. We have eight clients on Zoho Books and the workflow is identical.
Do I need to upload e-invoices separately or do they flow into GSTR-1?
E-invoices generated via the IRP automatically flow into your GSTR-1 — the GSTN system pulls them from the IRP database. Your job is to make sure your Tally has the same set of invoices that the IRP has. The reconciliation step in minute 0-10 above is exactly this check.
Want this Tally-to-portal workflow built into your accounting software?
We build the reconciliation, HSN validation, and JSON generation pipeline directly into Tally TDL or as a Zoho Books custom report — for SMBs filing 200 to 4,000 invoices a month. Typical engagement: 9 working days, fixed scope. First call is with the engineer who would write your TDL or Deluge code.
Book a 30-min Workflow CallFor a broader view of where we sit in the Indian tax-tech stack, our founder Vivek Singh writes on the same beat with a more first-person founder angle. Email us at contact@softechinfra.com if you want the GSTR-1 audit checklist sent before our call.
