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 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 Clients and select the relevant client on the invoices. On the Details tab, remove the postal code and save. Then, re-enter the postal code and save the profile.