I have added a Types multicheckboxes field and want to add two custom validations to this field:
–The first one is to make the field required
–The second one is to force the client to select maximum two checkboxes

jQuery(document).ready(function() {
\This adds the validation method to our API so that CRED can recognize it
    jQuery.validator.addMethod("maxselections", function(value, element, param) {
                                var element_name = jQuery(element).attr('name');
                                return (jQuery('input[name="' + element_name + '"]:checked').length !=0 &&jQuery('input[name="' + element_name + '"]:checked').length <= param[1]);
                              });
\This adds the validations methods as attributes on the element itself.                               
    jQuery('input[name="wpcf-postscheckboxesfield[]"]').attr('data-wpt-validate', '{}')
        .data('wpt-validate', {
          maxselections: {
            args: {
              1: 2
            },
            message: 'You have to choose at least 1, maximum two items'
          }
    }); 
     
});