Class 'GuzzleHttp\Client' not found
Just a quick guess, but here is what I have on a project I am working on.    

$client = new \Guzzle\Http\Client();
$request = $client-&gt;get($url);


yours

$client = new \GuzzleHttp\Client();


mine

$client = new \Guzzle\Http\Client();


I have \Http\Client - maybe you are just missing the slash?