If you've upgraded to Drupal 8.5.x and above, and have used Composer to install Drush 9, you will find that commands that use Acquia Site Aliases no longer work. Drush 9 is a complete rewrite of Drush, and the alias file format is now completely different.

Acquia provides downloadable Drush Aliases that are compatible with Drush 8 and 9, and allow you to run a shell command on a remote server.

When you are logged in to cloud.acquia.com, you can also use this script for all of your sites and extract the archive into $HOME

$ tar -C $HOME -xf $HOME/Downloads/acquia-cloud.drush-aliases.tar.gz

Log in to https://accounts.acquia.com/ and visit your profile then choose Credentials the link to download the Drush alias is under the Drush Integration codeblock. 

See https://www.drush.org/ for more information about using Drush 9.