Paginating single posts

Hello,

I’m trying to paginate a single post using the

<!--more-->

tag in the text editor in the post and in the single.php I have

<?php wp_link_pages(); ?>

or

<?php wp_link_pages( array( 'before' => '<div class="page-link"><span>' . __( 'Pages:','themnific') . '</span>', 'after' => '</div>' ) ); ?>

As it’s on the Themnific Noxon theme.

So I don’t understand why it’s not working. The page just displays the whole post as normal.