Missing XMLReader in my PHP version?

run php -m to check if the module is present

To install in debian based systems.

sudo apt install php7.2-xml

of course replace the php version with the version you are using.

You can check current used php version with :

php -v

After it is installed you will need to restart apache service if you are using it, or nginx.

sudo service apache2 restart

You have no XML extention installed. In RedHat like systems type yum install php53-xml in terminal. Or you can simply add phpinfo(); to your PHP code to rewiew your server configuration and find wether XML installed or not.