It is possible to import barcodes from tickets you sold through another system and scan them with the GUTS Scanner. You can import a CSV file in a specific event via Scanning > External Tickets. After importing, you can scan your external tickets with the GUTS Scanner.
The structure of the CSV file should either be a single column containing the barcode or contain the column named 'barcode' (without quotes).
You can see how many tickets are imported and how many of them have been checked in.