To retrieve an unpaid transaction, simply tap on the Transaction button.
All opened transactions will be listed under All Unpaid.
Under the Last 10 Transaction, you will find the last 10 paid or unpaid bills.
To retrieve transactions earlier than that, find it under Settings -> Previous Receipts.
To retrieve an unpaid transaction by a table, simply tap on the Table button.
It gives you an overview of all your table status in a listing format.
To view only the occupied tables, tap on the Occupied Table.