The invoice needs checking to see if it has been matched, if it hasn't then this can be reversed.
To reverse the invoice :
From LAD go to the Enquiries tab.
Select Transaction Enquiry.
Either search all Suppliers by picking the radio button Supplier.
You can also put in the Audit or Batch number from the transaction.
Select Search.
When the transactions come up highlight the correct one and select at the right hand side Reverse.
NB
After the posting is done check to make sure that the posting values for the reversals are correct on both the Supplier and the matter.