Did not install

[deckside]

Magento 2.2.2

Tried to install using
composer require php-cuong/magento2-newsletter-popup

This is the response

Using version ^2.1 for php-cuong/magento2-newsletter-popup
./composer.json has been created
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for php-cuong/magento2-newsletter-popup ^2.1 -> satisfiable by php-cuong/magento2-newsletter-popup[2.1.0].
    - php-cuong/magento2-newsletter-popup 2.1.0 requires magento/module-backend 100.0.*|100.1.* -> no matching package found.

Potential causes:
 - A typo in the package name
 - The package is not available in a stable-enough version according to your minimum-stability setting
   see <https://getcomposer.org/doc/04-schema.md#minimum-stability> for more details.

Read <https://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.

Installation failed, deleting ./composer.json.
root@ip-172-31-3-249:/var/www/magento/bin#