Hi Cees,
Please be aware that site
is an object, contact
and ct_locatie
in this case is the property of that object.
If you want to pass the field ID as a string, you can add just ct_locatie
{{ mb.map( 'ct_locatie', '100%', '480px', '14', '', 'Solexverhuur Woudenberg', 'Hier vindt je onze locatie' ) }}