How to add new tab in user edit page drupal
You just need one item only. Please make the following change

$items['user/%user/invoice'] = array(
    'type' =&gt; MENU_LOCAL_TASK,
    'title' =&gt; 'Subscription Invoice',
    'page arguments' =&gt; array('user', 1),
    'page callback' =&gt; 'usermail_invoice',
    'access callback' =&gt; 'user_is_logged_in',
    'weight' =&gt; 3 
);