If you rejected a Purchase Invoice Register transaction before un-matching the purchase order, follow these steps to un-match it:
Log in to Dimensions.
Click Creditors.
Under the Invoice Register section, click Match.
Click Match Orders.
Enter the order details and tick Include Matched Invoices.
Double-click the order to open it.
Deselect the matched lines.
Click the green tick to save the changes.
Click Creditors.
Under the Invoice Register section, click Amend Entry.
Locate the invoice in the list.
Double-click the invoice to open it.
Click the Save icon to update it.
Match the invoice to the order again. This resubmits it for approval.
If this is unsuccessful, contact support. See Get support in Dimensions.