How do I create a fixed agency fee on a plan item?

Navigate to a campaign and to a plan item for which you want to create a fixed fee.
Open the inspector panel on the right-hand side of the plan by double-clicking on one of the columns containing information on fees, e.g. total fee or fixed fee. You may need to display this column first.
Click on the "+Fixed fee" button to create a new fixed fee.
Assign a fee description.
Select an "Agency Fee Type". The entries displayed here can be configured in the reference data. See also Where do I add the Agency Fee Types?
Enter a fixed price.
Click on the "Save" button.
The fixed fee is now stored in the plan item. In contrast to the other fees, there is only one fixed fee and therefore no differentiation between forecast and realised.