[A] In order to do so, click on Tally Integration  >> Ledger Settings

[B] Now scroll down and search Default Tax Ledgers (Input) & Default Tax Ledgers (Output). In here Input is for purchase and output is for sales invoice.

[C] Now select the tax percentage for which you want to add ledger and click on "Edit/Delete", after that a window will slide from right side add ledger name it and click on "Save Details"

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