I normally use plugin_url() method to achieve enqueue.

function Zumper_widget_enqueue_script()
{   
wp_enqueue_script( 'my_custom_script', plugins_url('js/jquery.repeatable.js', __FILE__ ), '1.0.0', false );
}
add_action('admin_enqueue_scripts', 'Zumper_widget_enqueue_script');

I normally use plugins_url() method to achieve enqueue.

function Zumper_widget_enqueue_script()
{   
    wp_enqueue_script( 'my_custom_script', plugins_url('js/jquery.repeatable.js', __FILE__ ), '1.0.0', false );
}
add_action('admin_enqueue_scripts', 'Zumper_widget_enqueue_script');