GSTR-1 is a critical GST return that captures outward supplies (sales) of a registered taxpayer. A GSTR-1 mismatch occurs when the data filed in GSTR-1 does not align with:
Books of accounts
GSTR-3B
GSTR-2A / GSTR-2B (recipient view)
GST portal validations
Such mismatches can result in notices from GST authorities, ITC denial to customers, penalties, and compliance risks.
This knowledge base article explains why GSTR-1 mismatches occur, how to identify them, and how to correct them systematically.
GSTR-1 data is generated from:
Sales vouchers
Credit/Debit notes
Advance receipts and adjustments
Export and SEZ transactions
Mismatch happens due to:
Incorrect classification of invoices
Differences in tax rates or taxable values
Timing differences between returns
Errors in GSTIN, invoice number, or date
Manual changes on GST portal not reflected in books
Customer complaining about ITC not reflecting
GST notice for mismatch between GSTR-1 and GSTR-3B
Difference between Tally data and GST portal
Annual return (GSTR-9) reconciliation issues
Audit or departmental scrutiny
Sales voucher not included in GSTR-1
Voucher marked as non-GST
Incorrect voucher date (outside return period)
Same invoice number used twice
Manual re-upload of already filed invoices
Copy-paste errors in accounting software
Wrong customer GSTIN
Typographical errors
Inactive or cancelled GSTIN used
Invoice date in books differs from portal
Financial year mismatch
Incorrect invoice numbering series
Wrong GST rate applied
Rounding off differences
Manual override of tax values
B2B invoice reported as B2C
B2C Large/Small misclassification
Unregistered party treated as registered
Credit note not linked to original invoice
Wrong reporting month
Incorrect tax adjustment
Wrong supply type selected
LUT/Bond details missing
IGST paid vs without payment mismatch
Amendments done in books but not updated in GSTR-1
Incorrect amendment period selected
Invoices edited directly on portal
Data mismatch with accounting software
Lack of synchronization
Compare:
Sales Register vs GSTR-1
GSTR-1 vs GSTR-3B
GSTR-1 vs GSTR-2A / 2B
In accounting software:
Open GST Returns
Select GSTR-1
Check Error / Incomplete Vouchers
Check:
Invoice number
Invoice date
GSTIN
Taxable value
Tax rate
Place of supply
Edit voucher details
Correct GST classification
Fix tax ledger mapping
Ensure proper voucher type
Recompute GSTR-1
Regenerate JSON
Upload corrected data
Use Amended Invoices / Credit Notes
Do not delete already-filed data
Amend in next return period
Invoice Number Invoice Date Customer GSTIN Taxable Value CGST / SGST / IGST Place of Supply
| Issue | Root Cause | Fix |
|---|---|---|
| ITC not reflecting to customer | GSTIN mismatch | Correct GSTIN & amend |
| GSTR-1 vs 3B difference | Wrong tax rate | Recompute tax |
| Duplicate invoices | Same invoice number | Amend or delete duplicate |
| Portal rejection | Invalid data | Validate & re-upload |
| Missing credit note | Not reported | Report in amendment |
| Export error | Wrong supply type | Correct export settings |
Restrict GST data editing access
Enable audit logs in accounting software
Lock periods after filing
Maintain secure backups before amendments
Avoid portal-only changes without book updates
Reconcile GSTR-1 monthly
Use standardized invoice numbering
Avoid manual GST portal edits
Train staff on GST voucher entry
Validate data before filing
Maintain amendment tracking register
Backup data before GST filing
Cross-check with GSTR-2B regularly
GSTR-1 mismatches are primarily caused by data entry errors, classification mistakes, timing differences, and manual interventions. Regular reconciliation, disciplined accounting practices, and correct amendment procedures help ensure accurate GST compliance and reduced audit risk.
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