WP Query Shortcode -- Custom Post type using Custom Taxonomy

snippet.php

// create shortcode with parameters so that the user can define post queries
add_shortcode( 'recurring-events', 'recurring_events_parameters_shortcode' );
function recurring_events_parameters_shortcode( $atts ) {
    ob_start();

    // define attributes and their defaults
    $a = shortcode_atts( array (
        'type' => 'recurring_event',
        'posts' => -1,
        'categories' =>  '',
    ), $atts );

    // Check if category value is a single value or comma separated list. If the list is comma separated, create an array of values to be used.
    $terms = $a['categories'];
    if (!is_array($terms)) {
        $terms = explode(',', $a['categories']);
    }

    // define query parameters based on attributes
    $args = array(
        'post_type' => $a['type'],
        'posts_per_page' => $a['$posts'],
        'tax_query' => [
            [
                'taxonomy' => 'recurring_event_categories',
                'field' => 'slug',
                'terms' => $terms,
            ],
        ],
    );

    $query = new WP_Query( $args );
    if ( $query->have_posts() ) { ?>
        <div class="recurring-events">
            <?php
            print_r($terms);
            ?>
            <div class="fusion-row">

                <div class="recurring-events--listing">

                    <?php while ( $query->have_posts() ) : $query->the_post(); ?>

                    <div class="recurring-events--event">

                        <h2><?php the_title(); ?></h2>

                    </div>

                    <?php endwhile;
                    wp_reset_postdata();
                    ?>

                </div>

            </div>

        </div>
        <?php
       return ob_get_clean();
    }
}