How do I fix an "Invoice in use" message on PlusPoint when no one is working on the invoice?

How do I fix an "Invoice in use" message on PlusPoint when no one is working on the invoice?

Should it happen that PlusPoint keeps showing the "Invoice in Use" message although no one is working on the invoice and a shift needs to be closed the below steps need to be followed: 

1. System Lockout
In order to release this invoice a POS lockout is required.
  1. Access PlusCentral and navigate to Administration -> General Administration -> System Configuration.
  1. Click on the "Point of Sale" tab and find the option for the "Lock out POS Terminals for maintenance" setting.
  1. Select the "Change" button at the top of the page and activate this setting, click on the "Save" button.
  1. Thereafter wait 20 seconds for PlusPoint to close on all workstations.
  1. Remove the lockout option as explained above and re-save. Access PlusPoint and the invoice should be unlocked for the user to close and run their shifts and/or End Of Day process as normal.