Prevent Duplicate Vouchers
You can use the following option in Tally ERP to prevent upload of duplicate Vouchers
1. Gateway of Tally || Accounts Info || Voucher Types || Alter
2. Next, select the Voucher type (say Sales or Purchase)
3. Next, set the Voucher Numbering to "Manual"
4. Next, set the option Prevent duplicates as "Yes"
PS:
The "Prevent duplicates" option is enabled only if there are no entries for that voucher-type in your Tally Company.