Add custom post type to the loop (Underscores theme)

I am using custom post type UI plugin and I want to add custom post type of ‘formules’ in the loop on my front page, but every time I try to add I get a blank page. I also want to add more than one custom post types to the loop. I am not sure what I am getting wrong and I would appreciate some help.

My code is:

<?php if ( have_posts() ) : ?>
<?php /* Start the Loop */ ?>
<?php
$query = new WP_Query( array( 'post_type' => array( 'formules' ), 'tag__not_in' => array( 20 )) )
while( $query->have_posts() ):
$query->the_post();

get_template_part( 'content', get_post_format() );
?>

<?php endwhile; ?>

<?php googie_theme_paging_nav(); ?>

<?php else : ?>

<?php get_template_part( 'content', 'none' ); ?>

<?php endif; ?>