I am trying to only post one post of each custom taxonomy `APP_TAX_STORE` my `wp_query` looks like this:

    // show all alternative active coupons for this category from related store

                    $tax = get_the_terms($id, 'coupon_category');
                    $args = array(
                        'post_type' => APP_POST_TYPE,
                        'post_status' => 'publish',
                        'posts_per_page' => 5,
                        'meta_key' => 'clpr_topcoupon',
                        APP_TAX_TAG => 'gutschein',
                        'orderby'  => array(
                            'meta_value_num' => 'DESC',
                            'post_date'      => 'DESC',
                            ),                      
                        'tax_query' => array( 
                        'relation' => 'AND',
                            array(
                            'taxonomy' => 'coupon_category',
                            'field'    => 'slug',
                            'terms'    => $tax[0]->slug, 
                            ),
                            array(
                            'taxonomy' => APP_TAX_STORE,
                            'field'    => 'slug',
                            'terms'    => $term->slug,
                            'operator' => 'NOT IN',
                             ),
                        ),  
                    );
                    $query = new WP_Query( $args );
                    while ( $query->have_posts() ) :
                        $query->the_post();
                        get_template_part( 'loop', 'coupon' ); 
                    endwhile;
                    wp_reset_postdata();
Now I need to tell the loop to only show one post of each `APP_TAX_STORE` (taxonomy). 

I do know that I probably need a second query and that I have to combine then. However I tried so many solutions from this forum that I am know totally lost.

With this query I can call one post of each `APP_TAX_STORE`

    $terms = get_terms(array('taxonomy' => APP_TAX_STORE)); 
    foreach ($terms as $term){
        $args = array(
        'post_type' => APP_POST_TYPE, 
        'posts_per_page' => '1',
        'order_by' => 'date', 
        'order' => 'ASC', 
        'tax_query' => array(
            array(
                'taxonomy' => APP_TAX_STORE,
                'field' => 'slug',
                'terms' => $term->slug, 
                )
            )
        );
        $new_query = new WP_Query ($args);
        if ($new_query->have_posts()) {
            while($new_query->have_posts()){
                $new_query->the_post();
                get_template_part( 'loop', 'coupon' ); 
    					
            }
        }
      
    }

Now I need to combine these!

Really appreciate some help!