Class 'DOMDocument' not found

You need to install the DOM extension. You can do so on Debian / Ubuntu using:

sudo apt-get install php-dom

And on Centos / Fedora / Red Hat:

yum install php-xml

If you get conflicts between PHP packages, you could try to see if the specific PHP version package exists instead: e.g. php53-xml if your system runs PHP5.3.

PHP8: (latest version)

sudo apt-get install php8.0-xml

PHP7:

sudo apt-get install php7.1-xml

You can also do:

sudo apt-get install php-dom

and apt-get will show you where it is.

PHP 7.0:

• Ubuntu: apt-get install php7.0-xml
• CentOS / Fedora / Red Hat: yum install php70w-xml

PHP 7.1:

• Ubuntu: apt-get install php7.1-xml
• CentOS / Fedora / Red Hat: yum install php71w-xml

PHP 7.2:

• Ubuntu: apt-get install php7.2-xml
• CentOS / Fedora / Red Hat: yum install php72w-xml

PHP 7.3:

• Ubuntu: apt-get install php7.3-xml
• CentOS / Fedora / Red Hat: yum install php73w-xml

PHP 7.4:

• Ubuntu: apt-get install php7.4-xml
• CentOS / Fedora / Red Hat: yum install php74w-xml

PHP 8.0

• Ubuntu: apt-get install php8.0-xml
• CentOS 8 [with php:remi-8.0 enabled]: dnf install php-xml