The issue with the Z-report displaying zero could be due to a bug that occurs when an order is initiated on one terminal and completed on another within the same location.
To rectify this, you'll need to close all registers for the day and then regenerate the Z-reports. Please note that Z-reports can be generated from the terminal for the past 30 days.
If you need to generate a Z-report older than 30 days, you'll have to create a Summary report from the Portal.