Usage Scenarios

Purchase Documents

The check for duplicate amounts will be performed on post of a Purchase Order (Invoice or Receive and Invoice options), Purchase Invoice and Purchase Credit memo.
If the amount of the document you are posting is the same and within the period you specified in the Check for Duplicate Invoice Amount in Period field on the Purchase & Payables Setup you will receive a message similar to :

You need to accept the warning and then check that this is not a duplicate invoice or credit memo. If it is not, then set the Skip Check for Invoice Amount field on the Invoice Details tab to Yes.

You can now post the Invoice or Credit Memo as usual.