User has invoices that are missing the last digit of the Canadian postal code.
This might be due to the incorrect selection of the postal code mask in Global Settings > Custom Labels. You must select the correct zip or postal code mask here. Check CORE Help Center for details. If this does not fix the issue, go to Contacts > Clients and select the relevant client on the invoices. On the Details tab, remove the postal code and save. Then, re-enter the postal codes and save the profile.