Liquid code in Betty Blocks platform cannot be parsed

Question

I am working in a Betty Block platform (low-coding). In this framework there is a possibility to work with Liquid. So I made the next code:

 present?(var:name) ?
    present?(var:voorvoegsel) ?
        var:voor_let_nat_p + " " + var:voorvoegsel + " " + var:name
    :
        var:voor_let_nat_p +" "+var:name
:
present ?
    (var:company_name) ?
        var:company_name
    :
        "Niet gevonden"

The Liquid parser of Betty Blocks claims this is a not valid code, but I cannot imagine why. Does somebody see an error which I overlooked? I do not have more error details.