I need to import listings into the Listeo theme of Wordpress using WP All Import plugin. All works fine, however, I am unable to import values for custom fields which have a type of Checkbox.

I've tried different syntaxes in the csv file:

1
on
['1']
['on']

but none seems to work. The field is empty once the upload is completed. Google search provides no answer. I am not using ACF.