Wastage internal references are used to link the wastage lines that are imported from your tills to the wastage monitor, the below steps will also allow you to fix the flash import sales error message:
No monitor linked to flash, (ID) with internal reference (reference shown on till file)" at the (site name).
Click the Admin Cogs
icon along the top bar.Click Waste Management, then click Waste Monitors.
Locate the monitor and click the Edit button to access the monitor.
From the details tab locate section Internal References and enter the references 1 per line.
Click the Update button at the bottom of the page to save any changes.