how can I correct an incorrectly posted payment on account from a previously VAT reconciled period?

Sage set up to calculate VAT returns using the cash accounting method (otherwise this wouldn't be a problem)
- This is a payment on account posted to a supplier account ( you don't say whether this is on the customer or supplier ledger, so if it is on the customer ledger just mirror these steps)
- You need to remove the payment on account from the supplier and bank ledgers (if it's just the value that is wrong, follow these steps to remove it, then post it correctly)
You need to reduce (debit) the balance of the purchase tax control account, and also correct the balance on the supplier ledger account.
When using the cash accounting method in Sage, you can only allocate transactions to each other if they have the same T code.

Post a dummy invoice to the supplier ledger using nominal code 9998 (suspence) and tax code T1, with the Net and VAT amounts matching your incorrect payment on account. Use the detail field for some explanation. This will adjust the balance on the suuplier account. You can allocate the Payment on Account against the dummy invoice via Bank, Supplier.

Post a bank receipt in the relevant bank account, nominal code 9998, and tax code T1 to reverse the bank entry. You can allocate the incorrect payment against the dummy bank receipt in the bank reconciliation screen.

Your suspense account balance will now be nil, the bank balance is corrected and the VAT value of the correction will be posted in the sales tax control account.

The dummy invoice in the suuplier ledger will not appear on the VAT return calculation, but the bank receipt will, so it should increase the VAT liability by the overclaimed amount.

Posted in: book-keeping,bookeeping,line 50,sage line 50