Clean the sales register before anything is uploaded

The hard part of GSTR-1 is not typing figures into boxes. The hard part is knowing that the figures are clean before they are reported. Once sales data is filed, every duplicate invoice number, wrong GSTIN or mismatched tax head has a longer route back to correction.

Treat the preparation stage as its own workflow. Export the sales register, compare it with your books, classify each supply, and only then prepare the return data. The GST filing preparation tool is meant for that pre-filing discipline: working through the register locally before the data becomes somebody else's mismatch.

This is not a walkthrough of a government portal and it is not tax advice. Deadlines, thresholds, schemas and validation rules change, so keep a filing calendar and confirm the current requirements for your registration and supply type.

Start with reconciliation, not upload

Your invoice register should agree with the books before anything is uploaded. That means checking that every issued sales invoice appears in the register, the taxable value and tax amount match the accounting records, cancellations have been handled properly, and credit or debit notes have not been left in a side file.

Reconciliation is easier when you use stable identifiers. Invoice number, invoice date, recipient GSTIN, taxable value and tax amount should be enough to trace a row back to the source document. If a row cannot be traced, do not "park" it for later and keep going; investigate while the month is still fresh.

The point is to catch preparation errors before they become filing errors. A missing invoice found before filing is a correction to your working sheet. The same missing invoice found months later may mean amendments, explanations and customer follow-up.

Classify B2B, B2C-large and B2C-small correctly

Classification changes what detail is reported and how it will be matched. A registered recipient generally belongs in B2B reporting, where invoice-level details and GSTIN accuracy matter. B2C-large supplies are reported with more detail because their value and place-of-supply treatment make them significant. B2C-small supplies are aggregated differently.

Do not classify from customer name alone. Use the recipient GSTIN, supply value, place of supply and the current reporting rules. A sale to a familiar business without a valid GSTIN in your records is not the same data problem as a sale to a registered business with a verified GSTIN.

The distinction matters because it affects matching, tax-head treatment and the summary totals. A row in the wrong bucket can make the return look balanced while still being wrong in the section that matters.

Bring notes, exports and nil-rated supplies into the same view

The invoice register is only part of the story. Credit notes and debit notes change earlier invoices and need their own attention. Each note should connect back to the original document, carry the right date and amount, and be included in the period where it belongs.

Exports need separate handling because the recipient, currency, shipping bill and tax treatment may differ from domestic sales. Nil-rated, exempt and non-GST supplies should not be mixed into taxable outward supplies just because they also appear in sales. They still belong in the preparation file, but they need the right label.

The same applies to amendments from earlier periods. Keep them visible as amendments rather than rewriting the past in your working register. That makes the audit trail easier to explain and reduces the chance of accidentally filing the same correction twice.

Check HSN and document series summaries

GSTR-1 preparation is not only invoice rows. You also need the HSN summary and document series summary to make sense.

For the HSN summary, check that descriptions, quantities, units, taxable values and tax amounts group correctly. Old item masters often carry outdated or over-general codes, especially in small businesses where the same spreadsheet is copied each year. Review the codes before summary generation rather than after a total looks strange.

For the document series summary, list the invoice, credit note, debit note and other document ranges issued during the period. Missing, duplicated or skipped numbers should be explained by your records, not discovered when a summary count does not match.

If you need a readable copy of a CSV export for review, use the CSV to PDF tool to turn the working data into a paginated report without sending the sales register to a conversion service.

Failure modes worth catching early

Some mistakes are so common that they deserve their own pass:

• A GSTIN with a wrong checksum. It may look plausible to a human and still fail validation.
• A duplicated invoice number. This often comes from parallel spreadsheets, branch series or a copied template.
• A missing invoice number. Gaps need an explanation before filing, not after.
• Place-of-supply mismatch. The wrong state can produce the wrong tax head, especially when billing and delivery addresses differ.
• CGST plus SGST where IGST should appear, or the reverse. The total tax may look right while the component is wrong.
• Amendments to earlier periods buried in current sales. Keep them separate so they are reported as amendments.

These checks are dull, but they prevent the most expensive kind of filing work: reconstructing what happened after a notice or customer mismatch arrives.

Keep the register local while you prepare

A sales register is commercially sensitive. It contains customer names, GSTINs, item lines, prices, discounts, credit notes, sales volume and sometimes export details. That is enough to describe the shape of the business.

Preparing it on-device keeps the working copy under your control. The document bytes are not sent to a conversion server just to classify rows, produce review PDFs or assemble support material. You still need backups, access control and a deadline calendar, but the cleaning stage does not need to happen inside a web account.

Clean invoices also make preparation easier. If your source bills are weak, start with the GST invoice workflow so place of supply, tax split, serial number and recipient details are captured correctly at the point of issue.

A pre-filing preparation checklist

• Reconcile the invoice register against the books and bank-supported sales records.
• Validate GSTINs before classifying B2B rows.
• Separate B2B, B2C-large and B2C-small supplies using current rules.
• Include credit notes, debit notes, exports, nil-rated supplies and amendments.
• Check place of supply and tax heads before totals are finalised.
• Review HSN and document series summaries before filing, not after.