Sometimes the orders are importing to the system in an incorrect way and you need to remove the invoice that was created against the order. 

In that scenario, first the unnecessary invoice needs to be removed from the A/C system. 

Once it is removed open the order, go to Shipments\Invoices tab; right click on the invoice that needs to be removed and select the option "Remove":

Please contact The Order Exchange Support if there are any further issues or questions.