Data is not being added to the new field?

Question

WordPress

There are 2 types of records clients and projects, it was necessary to link these types of records
than the issue was resolved through metabox and post_parent everything works fine, but there is 1 more record type that needs to be associated with the rest, as we know the post_parent field is index and cannot be multiple, so I decided create a new field in the database let's say post_svyazka
added 1 more metabox but the data is not written, what could be wrong?
metabox code

add_action('add_meta_boxes', function () {
  add_meta_box( 'otrasli', 'Отрасль продукции', 'otr_team_metabox', 'products', 'side', 'low'  );
}, 1);

// метабокс с селектом команд
function otr_team_metabox( $post ){
  $teams = get_posts(array( 'post_type'=>'otrasli', 'posts_per_page'=>-1, 'orderby'=>'post_title', 'order'=>'ASC' ));

  if( $teams ){
    // чтобы портянка пряталась под скролл...
    echo '
    <div style="max-height:200px; overflow-y:auto;">
      <ul>
    ';

    foreach( $teams as $team ){
      echo '
      <li><label>
        <input type="radio" name="post_svyazka" value="'. $team->ID .'" '. checked($team->ID, $post->post_svyazka, 0) .'> '. esc_html($team->post_title) .'
      </label></li>
      ';
    }

    echo '
      </ul>
    </div>';
  }
  else
    echo 'ничего  нет...';
}