apache 2.2 - PHP code being displayed in clear text?

Setting up my first ever server from scratch for a
migrated Wordpress site. It's been a long journey, but I'm almost at the end of
this.

This is what I've done so
far.

• Created the GCP micro
  instance.



• This tutorial on how to setup the
  LAMP stack. - href="https://www.digitalocean.com/community/tutorials/how-to-install-linux-apache-mysql-php-lamp-stack-on-debian"
  rel="nofollow
  noreferrer">https://www.digitalocean.com/community/tutorials/how-to-install-linux-apache-mysql-php-lamp-stack-on-debian


• Followed
  a tutorial on how to setup virtual hosts - granted I'm still just trying to get the
  primary domain setup. (Can't post the link due to reputation level on
  ServerFault)


• Migrated my Wordpress database into the new
  instance.


• Edited my config files with the updates (I'm
  99.9% wordpress is configured correctly now after having gone through many tutorials and
  troubleshooting).

When I
hit the website - what I get instead is just clear text of the wordpress code to the
site. This is strange also because my /wp-admin/ part of the site seems to be
initializing the PHP.

I've managed to open up
the apache log files and I find this fatal error that I believe is causing the
problem:

[Wed Jun 07 16:50:45.835692 2017] [:error] [pid 22258] [client

181.199.83.55:49298] PHP Fatal error: Class 'OO_Api' not found in
/var/www/argineconsul.com/public_html/wp-content/plugins/online-outbox-subscription-form/includes/controller.php

on line 7

Is the
reason PHP failing is because of this one plugin? Or is the PHP not rendering for
another reason?

Any help would be greatly
appreciated! My server is at: http://35.188.216.56/ .