assuming all your constants are correct, it should just look like this
$terms = get_terms(array('taxonomy' => APP_TAX_STORE));
$tax = get_the_terms($id, 'coupon_category');
foreach ($terms as $term) {
$args = array(
'post_type' => APP_POST_TYPE,
'posts_per_page' => '1',
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,
),
)
);
$new_query = new WP_Query ($args);
if ($new_query->have_posts()) {
while ($new_query->have_posts()) {
$new_query->the_post();
get_template_part('loop', 'coupon');
}
}
}