Create multipage post

I want to create a multipage post. I’ve tried ‘<!–nextpage–>’ and ‘<?php wp_link_pages(); ?>’ as described here https://codex.www.ads-software.com/Styling_Page-Links. So far it hasn’t worked.

Just to be clear I’ve only looked at this as preview. I haven’t published the post to test this. I’ve inserted the tags in text mode.

I’m on version 2.4 of the WP-Creativix theme because we made some changes to the original theme that would be lost in an upgrade.

I hope someone has the answer for me. Thanks in advance!