In the mobile app, it will be easy to tell which receipts have been synced with Saasu because a “saasu” icon will appear next to the receipt.
In the web portal, navigate to your company "Solid Kit" on the left navigation menu. Click on your name and you will see a list of receipts. Those that have been synced to Saasu will have the "saasu" icon as well.
The best practice is to archive those that have been synced instead of deleting them. That way they can be easily accessed at a later date if need be.