cURL error 6: Could not resolve host

I am trying to make a a login method that returns a password grant token to the user to use with an iPhone app. I am using Guzzle like this

$response = $http->post('http://www.srty.test/oauth/token', [
            'form_params' => [
                'grant_type' => 'password',
                'client_id' => env('PASSWORD_GRANT_CLIENT'),
                'client_secret' => env('PASSWORD_GRANT_SECRET'),
                'username' => request('email'),
                'password' => request('password'),
                'scope' => '',
            ],
        ]);

calling it I get this error cURL error 6: Could not resolve host but the URL is a valid url