Let's why this is happening, Kay84.
You might have not marked the Show Items table for expenses in your Account and Settings. Here's how:
That should allow you to see the costs of the billable items. Also, I'd recommend reviewing the affected items. Then, ensure that the costs were already added. Here's how:
Let us know how this goes so we can further assist you. Additional details such as screenshots or error messages would be much appreciated. Have a great day!