How do I put tax_query in this WP_query?

So I have a WP_Query, that displays posts from a custom post type. It only displays posts that have a date in the future, not ones that have past.

I now want to include tax_query in this WP_Query. So that it only displays custom posts that belong to a specific term, in a custom taxonomy called event categories. My code doesn’t seem to work since i’ve added the tax_query part. It doesn’t display any messages in the browser at all. How can I make it work with the tax_query part added please?

<?php 

  $args = array(
    'post_type' => 'event',
    'posts_per_page' => 100,
    'meta_query' => array( 'key' => '_start_ts', 'value' => current_time('timestamp'), 'compare' => '>=', 'type'=>'numeric' ),
    'orderby' => 'meta_value_num',
    'order' => 'ASC',
    'meta_key' => '_start_ts',
    'meta_value' => current_time('timestamp'),
    'meta_value_num' => current_time('timestamp'),
    'meta_compare' => '>=',
'tax_query' => array(
  // second array
    array(
      'taxonomy' => 'event-categories',
      'field'    => 'slug',
      'term' => $termst
    )
     // end second array
  ),

  );

  // The Query
  $query = new WP_Query( $args );

  // The Loop
  while($query->have_posts()):
  $query->next_post();
  $id = $query->post->ID;
  echo '<li>';
  echo get_the_title($id);
  echo ' - '. get_post_meta($id, '_event_start_date', true);
  echo '</li>';
  endwhile;

  // Reset Post Data
  wp_reset_postdata();

https://wordpress.org/plugins/events-manager/