Grid with Checkbox Column sdk sap b1 - I still get the Column as a Textedit and not as a checkbox

Hello,

I am trying to get a Grid with a Checkbox Column using Data from the System Table OCLG ( and the checkbox Field should be the OCLG.Closed Field)

I still get the Grid like on the photo below :

and i did it like that :

and here is my Datatable definiton :

any Idee why i still get the Grid-Column as a Textedit and not as a checkbox?