I have another way how you can check if you haven't missed marking a billable expense, JasperContracting.
We can pull up the Transaction List with splits report, then customize it so it will show the non-billable expenses. To do so, you can follow the steps below:
Go to the Report tab.
In the Find report by name bar, search the Transaction List with splits.
Click on Customize.
Select the Row/Columns and put a checkmark beside Billable.
Click on Filter, then choose Bill as a Transaction Type.
Select Run report.
Once you run the report, you'll now have the option to see in the Billable column "Yes" if the transaction is billable, while the column won't show anything if it's not marked as billable.