Failing to install Guzzle PHP

Hello! I am working with an API that recommends uses Guzzle for HTTP requests. I tried to install it using composer require guzzlehttp/guzzle:^7.0, but I get this error:

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - php-http/guzzle6-adapter v1.1.1 requires guzzlehttp/guzzle ^6.0 -> satisfiable by guzzlehttp/guzzle[6.0.0, 6.0.1, 6.0.2, 6.1.0, 6.1.1, 6.2.0, 6.2.1, 6.2.2, 6.2.3, 6.3.0, 6.3.1, 6.3.2, 6.3.3, 6.4.0, 6.4.1, 6.5.0, 6.5.1, 6.5.2, 6.5.3, 6.5.4, 6.5.5, 6.5.x-dev] but these conflict with your requirements or minimum-stability.
    - php-http/guzzle6-adapter v1.1.1 requires guzzlehttp/guzzle ^6.0 -> satisfiable by guzzlehttp/guzzle[6.0.0, 6.0.1, 6.0.2, 6.1.0, 6.1.1, 6.2.0, 6.2.1, 6.2.2, 6.2.3, 6.3.0, 6.3.1, 6.3.2, 6.3.3, 6.4.0, 6.4.1, 6.5.0, 6.5.1, 6.5.2, 6.5.3, 6.5.4, 6.5.5, 6.5.x-dev] but these conflict with your requirements or minimum-stability.
    - php-http/guzzle6-adapter v1.1.1 requires guzzlehttp/guzzle ^6.0 -> satisfiable by guzzlehttp/guzzle[6.0.0, 6.0.1, 6.0.2, 6.1.0, 6.1.1, 6.2.0, 6.2.1, 6.2.2, 6.2.3, 6.3.0, 6.3.1, 6.3.2, 6.3.3, 6.4.0, 6.4.1, 6.5.0, 6.5.1, 6.5.2, 6.5.3, 6.5.4, 6.5.5, 6.5.x-dev] but these conflict with your requirements or minimum-stability.
    - Installation request for php-http/guzzle6-adapter (locked at v1.1.1, required as ^1.1) -> satisfiable by php-http/guzzle6-adapter[v1.1.1].


Installation failed, reverting ./composer.json to its original content.