A duplicate payment is an additional payment made to a supplier that has already been paid. Duplicate payments are caused by flaws in an entity's accounts payable processes that do not detect the presence of prior payments. For example, the payables software should automatically detect a supplier invoice number for which a payment has already been made. The most common case in which duplicate payments occur is when a supplier invoice does not contain an identifying invoice number (as is frequently the case with periodic billings).
Some audit firms specialize in the detection of duplicate payments for their clients.