I tried to download google api using composer to a legacy code but, the following error appeared:
composer require google/apiclient:^2.0
./composer.json has been updated
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 google/apiclient 2.0 -> satisfiable by google/apiclient[v2.0.0].
    - google/apiclient v2.0.0 requires google/auth 0.8 -> satisfiable by google/auth[v0.8].
    - Conclusion: don't install guzzlehttp/psr7 1.4.2
    - google/auth v0.8 requires guzzlehttp/psr7 1.2.* -> satisfiable by guzzlehttp/psr7[1.2.0, 1.2.1, 1.2.2, 1.2.3].
    - Can only install one of: guzzlehttp/psr7[1.2.0, 1.4.2].
    - Can only install one of: guzzlehttp/psr7[1.2.1, 1.4.2].
    - Can only install one of: guzzlehttp/psr7[1.2.2, 1.4.2].
    - Can only install one of: guzzlehttp/psr7[1.2.3, 1.4.2].
    - Installation request for guzzlehttp/psr7 (locked at 1.4.2) -> satisfiable by guzzlehttp/psr7[1.4.2].
Installation failed, reverting ./composer.json to its original content.
What should I do?