Cannot get this plugin to work

Here is the code that I originally had, which gave me buttons for next and previous post. However, they were in date order, not what I wanted, and I couldn’t re-order the custom posts because there are over 450 of them.

<?php the_post_navigation(
				array(
					'next_text' => '<span class="post-title">%title <i class="fa fa-chevron-right"></i></span>',
                    
                    
					'prev_text' => '<i class="fa fa-chevron-left"></i> <span class="post-title">%title</span>',
				)
			);?>

Now when I tried the following, as per your documentation.

<?php previous_post_link_plus( array(

                         'order_by' => 'post_title',

                         'loop' => true,

                         'max_length' => 30,

                         'tooltip' => 'Previous post',

                         'in_same_cat' => true,

                         'ex_posts' => '5, 12'

                    ) );?> |

<?php next_post_link_plus( array(

                         'order_by' => 'post_title',

                         'loop' => true,

                         'max_length' => 30,

                         'tooltip' => 'Next post',

                         'in_same_cat' => true,

                         'ex_posts' => '5, 12'

                    ) );?>

It breaks the site saying that the site is experiencing technical difficulties. Please help, I’ve been trying to get my pages to show up in alphabetical order for a WEEK now.

Kind Regards
Vince Gledhill

The page I need help with: [log in to see the link]