Payment for transportation

I add transportation upon request:

Transport from/to the airport, upon request. The cost is 15 Euros from Airport and 15 Euros to Airport.

How can i get the money through booking payment?

I want the guests to pay in advanced, if they want the transportation

Thank you 

G Savvopoulos

Hi Aaltje, this issue is more complicated than I thought.
I had a long communication on phone, with employees of booking, almost an hour.
They had to make adjustments for my property, inside the system.
My experience says, that this issue needs help from professionals.