Fatal error: Call to undefined function mysqli_connect() in /home/user/public_html/includes/connection.php
MySQL Improved extension was disabled in the hosting environment.
Fix this error by enabling the MySQL Improved extension and recompiling the Apache via EasyApache.
The MySQL Improved extension is an improved version of the older PHP MySQL driver used in PHP to provide an interface with MySQL databases.
To enable Improved extension from WHM, refer to the following knowledgebase article - Enable/ Disable PHP Extensions using EasyApache