Hello,
In order to be able to Un'OK records, you need to have permisions:
Module System>>Settings>> Access groups:
Add action to your access group of "UnOK all records" - full
Than you can OK, un-ok records.
We advice to use this very carefully.
Better solution is to invalidate the record.
Open the wrong invoice, click on file menu >> Record>>Invalidate
Best regards,
Hansaworld support