Can I bring my books across from Tally?

Yes. In Settings, open Bring your data in and choose Move from Tally. Admins, leadership and finance people who can post to the books can do it. Margin starts your books on 1 April and brings your balances across as on 31 March.

Add your bank accounts in Margin first, so each bank's opening balance lands on the right account.

1. Customers, vendors and accounts. In Tally, export All Masters as XML (Data Interchange), with Language set to Default (All Languages), and upload the file. Every customer and vendor comes across with their GST number, state, PAN, address and credit days. If one might already be in Margin, you choose whether it's the same. Then match each Tally ledger to an account in Margin: Margin suggests one from its Tally group and remembers your choices.
2. Balances on 31 March. In Tally, export the trial balance as on 31 March, showing each ledger (F5), to Excel, and upload it. Type your closing stock from Tally's Balance Sheet. Margin builds one opening entry dated 1 April, which must balance: a difference of ₹100 or less goes to Opening balance adjustments. The entry waits in the Review inbox until someone approves it, and you can approve it yourself.
3. Open invoices and open bills. In Tally, export Bills Receivable and Bills Payable as on 31 March to Excel, and upload each. Each invoice and bill still open comes across with its Tally number and date, so payments can be matched to it and you can send reminders. Margin checks each customer's and vendor's bills add up to their balance in the trial balance. A customer or vendor whose bills Tally doesn't keep one by one comes across as one "Balance on 31 March" invoice or bill. These don't go into your GST or TDS returns, the Tally export or the Review inbox, and don't change your books: the opening entry already holds them. Automatic reminders leave them out until you switch them on in Receivables.

Nothing is saved until you confirm each step, and you can undo a step until anything uses what it brought across. Bank details, TDS details, stock items and cost centres don't come across, and sales, bills and payments since 1 April need entering in Margin.