var verifyPaymentType = function () {
//coloque os checkbox dentro de uma div com a class checkbox
var inputs = window.jQuery('.checkbox').find('input');
var first = inputs.first()[0];
inputs.on('change', function () {
this.setCustomValidity('');
});
first.setCustomValidity( window.jQuery('.checkbox').find('input:checked').length === 0 ? 'Choose one' : '');
}
window.jQuery('#submit').click(verifyPaymentType);
}