Fatal error: Uncaught Error: Call to undefined function yaml_parse_file()

The Y module does not reinvent the YAML wheel. You have to install the PHP YAML module.

Information on this module is at: https://www.php.net/manual/en/book.yaml.php

What it doesn't tell you, though, is that the Ubuntu ppa ppa:ondrej/php includes the PHP YAML module, so in Ubuntu, using this ppa installing the PHP YAML module may be as easy as:

sudo apt install php-yaml

though, if you use an older PHP version, you may need to do something like:

sudo apt install php7.4-yaml

Information on installing PHP modules for Drupal 7 / YAD7 server is at: https://yad7.org/content/setting-drupal-7-web-server-lemp-stack

Hi, Thanks, I will test this later on.
May be this module is in need of some documentation and installation instructions?
Greetings and great weekend!

The dependency of this module on the PHP / PECL YAML module has been noted and the documentation has been updated.