wp_insert_post not return post id

I am using wp_insert_post to add page on plugin activation.
Default wp_insert_post return page_id/post_id after create page/post.

my problem is that it’s not return page_id.

my code is

register_activation_hook( __FILE__, 'mytables_ll' );
function mytables_ll()
{
	$post_id = -1;

		$author_id = 1;
		$title = 'page1';
		$slug = 'page1';

		if( null == get_page_by_title( $title ) )
		{

			$post_id = wp_insert_post(
					array(
							'comment_status'	=>	'closed',
							'ping_status'		=>	'closed',
							'post_author'		=>	 $author_id,
							'post_name'		=>	 $slug,
							'post_title'		=>	 $title,
							'post_status'		=>	'publish',
							'post_type'		=>	'page'
					));

			update_post_meta($post_id, '_wp_page_template', 'template-form1.php');

		}
}

Anyone can help me what is problem.
Thanks in advance