Problem with guzzle

[mackiexx]

i am unable to use this.. this is the problem i'm having

Problem 1
- php-http/guzzle6-adapter[v2.0.0, ..., 2.x-dev] require guzzlehttp/guzzle ^6.0 -> found guzzlehttp/guzzle[6.0.0, ..., 6.5.x-dev] but it conflicts with your root composer.json require (^7.0.1).
- Root composer.json requires php-http/guzzle6-adapter ^2.0 -> satisfiable by php-http/guzzle6-adapter[v2.0.0, v2.0.1, v2.0.2, 2.x-dev].

Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.
You can also try re-running composer require with an explicit version constraint, e.g. "composer require berkayk/onesignal-laravel:*" to figure out if any version is installable, or "composer require berkayk/onesignal-laravel:^2.1" if you know which you need.