query multiple taxonomies

I have a function set up to show ‘Similar Products’, i.e. showing products that share the same products-category taxonomy term. This works great but I want to narrow the function even further and make it more specific. Thus I want it to look at 2 taxonomies (product-category and space) to find similar products. The current markup as follows:

    <?php  
    $terms = wp_get_post_terms( $post->ID, 'products-category' );
    if($terms){
      // post has course_type terms attached
      $course_terms = array();
      foreach ($terms as $term){
       $course_terms[] = $term->slug;
      }

     $original_query = $wp_query;
     $wp_query = null;
     $wp_query = new WP_Query(
        array(
            'posts_per_page' => '4',
            'post_type' => 'regularproducts',
            'tax_query' => array(
                array(
                    'taxonomy' => 'products-category',
                    'field' => 'slug',
                    'terms' => $course_terms, //the taxonomy terms I'd like to dynamically query
                ),
            ),
            'orderby' => 'title',
            'order' => 'ASC',
        )
    );

    if ( have_posts() ): ?>

    <?php while (have_posts() ) : the_post(); ?> //etc...

So it currently only looks at the products-category taxonomy for similar products (posts), but I want it to look at BOTH product-category and space to display more specific similar products, if possible. Any suggestions would be greatly appreciated!

First of all, get all term slugs from the custom taxonomy space by current post ID.

$space_terms = wp_get_post_terms( $post->ID, 'space' );
if( $space_terms ) {
  $space_terms = array();
  foreach( $space_terms as $term ) {
   $space_terms[] = $term->slug;
  }
}

You should specify the logical relationship between each inner taxonomy array when there is more than one.

The relation key in the array describes the relationship. Possible values are OR and AND.

'tax_query' => array(
    'relation' => 'OR',
    array(
        'taxonomy' => 'products-category',
        'field'    => 'slug',
        'terms'    => $course_terms,
    ),
    array(
        'taxonomy' => 'space',
        'field'    => 'slug',
        'terms'    => $space_terms,
    ),
),