See some instructions here: https://vip.wordpress.com/documentation/incorporate-co-authors-plus-template-tags-into-your-theme/
To As we use a variant of the Accesspress-lite theme, we'll need to do some custom coding to make this work. First, to put the blog into debug mode so we can see errors uncomment the following in wp-config.php
error_reporting(E_ALL); ini_set('display_errors', 1);
define( 'WP_DEBUG', true);
Then replace the old code with the replacement code in template_tags.php as follows:
Old code from template_tags.php