First you need to check if you are matching invoice to purchase orders in Dimensions Accounts or FocalPoint. You can do this by the following steps:
Log into Dimensions Accounts.
Click on System Tab.
Click Options Icon.
Click on Invoice Register Options.
Click on the Pop Approval tab.
If the Match in Focalpoint tick box is ticked. Then you are matching in FocalPoint otherwise you are matching in Dimensions Accounts.
If you are matching in Dimensions Accounts you can un-match using the following steps
Log into Dimensions Accounts
Navigate to the Creditors Tab.
Look for the Invoice Register Section.
Click on the Match Button.
Click on the Match Order option.
Tick Include Matched Invoices tick box
Go into the order and double-click the order line it will un-match the line.
Click on Tick icon