Nextpage cuts off post instead of multiple pages

Hi all, I’m using the WordPress 2012 theme on version 4.1

I put <?php wp_link_pages(); ?> in the single.php file within Editor, and have put in <!--nextpage--> within the text/html of my post where I want to add a second or third page.

However, the result is that wherever I first put the page break, the post is simply cut off without a second page link appearing.

I’m wondering if I didn’t put the <?php wp_link_pages(); ?> in the right place within the editor?

I watched it a video where it was placed at the very bottom. So I placed mine below
both <?php get_sidebar(); ?> and <?php get_footer(); ?>