Suggestions:
Advance adjustment in Purchase vouchers are designed for passing the advance receipts and payments. We can record hundred percent of the amount in advance against Purchase order.
Purchase voucher menu exists in Finance payables -> Purchase payables -> Voucher.
In advance adjustment tab users can add the values of advance payments done against Purchase order, tax allowed to be calculated manually. However the tax available in that period will be calculated. Posting of accounts are also done for the advance on confirming the voucher.