I'm using Bookit 2.1.3.

I'm using it for a meetingroom reservation.
I'm using supplement for Lunch options. (such as "Small lunc"h minimal 4 persons/ "Big lunch" 8 or more persons)

I want to be able to add a fixed amount (for example 4 dollar) to my supplement as delivery costs.
This amount should not increase when selecting more persons in the lunch.

Can you guys help me how to configure this?

reminder....