GST monthly return checklist (GSTR-1 and GSTR-3B)

What's needed each month to file GSTR-1 and GSTR-3B. Every item below, with where your client gets it.

Why clients should send it on time: GST returns filed late attract a late fee for every day of delay, plus interest on any tax due.

The checklist

1
Sales invoices
All sales invoices for the month, or the sales register from your billing software.
Where the client gets it: Export the month's sales from Tally, Vyapar or your billing app, or send the invoices as PDFs. A summary with invoice numbers, GSTINs and amounts is enough.
2
Purchase invoices
All purchase bills with GST, so we can claim input tax credit.
Where the client gets it: Photograph each bill with your phone, or forward the supplier's PDF. We need the ones with GST on them to claim input credit.
3
Credit and debit notes
Any issued or received this month.
4
Expense bills with GST
Rent, phone, internet, professional fees, etc.
Where the client gets it: Photograph each bill with your phone, or forward the supplier's PDF. We need the ones with GST on them to claim input credit.
5
Bank statement for the month
Every business account, as the PDF from your bank.
Where the client gets it: Net banking or the bank's app: Account statement → choose the dates → download as PDF (not a screenshot). SBI, HDFC and ICICI all have this under Accounts or Statements. One file per account.
6
Anything unusual this month? question
Exports, advances received, reverse charge purchases, a new branch? Type "none" if nothing.

Send the list as one link on WhatsApp. The client ticks items off as they upload, from their phone.
Each file is checked as it arrives: the right financial year, the client's own PAN, and locked AIS or bank PDFs opened.
Reminders go out until every item is in, and stop by themselves when it is.

Your client opens it on WhatsApp, uploads each item from their phone, and every file is checked as it arrives. First month free, no card.