I have tried installing the WP Live Chat Support plugin and also got the error. I looked up what is causing the error to show up and found a solution.
I have attached a .zip file called Mobile_Detect.zip. Download it, unzip the file Mobile_Detect.php and replace it with the file on your server located in wp-content/themes/elvyre/includes/libs/ folder.
You will now have access to your WordPress admin panel. Login and deactivate (maybe even delete) the plugin WP Live Chat and install it all over again.
Everything should work now normally.