How to fix Unable to install Softaculous extension in Plesk Onyx

Unable to install Softaculous extension: POSIX extension is not loaded in PHP , That because of The package
php-process
that is required for Softaculous is not installed on a server.

Install the required package:

# yum install php-process

Verify it is loaded:

# php -m | grep -i posix
posix

Now try to Install Softaculous again.