Before / After – wp_link_pages Not Working

Hi!

I am stumped by how to make my wp_link_pages work on my downloaded theme: https://jinsonathemes.com/fabs/?themedemo=Zylyz

Here is the bit of code that I assume calls it in my Single Post (single.php)
<?php wp_link_pages(array('before' => '<p><strong>Pages: </strong> ', 'after' => '</p>', 'next_or_number' => 'number')); ?>

Here is it running on my actual website: https://www.thatteacherguy.com/reaer/

Any ideas would be greatly appreciated ??