I’ve been trying to create an async request for a few days now, and I’m not succeeding either.. this is my code

require 'vendor/autoload.php';
use GuzzleHttpClient;
use GuzzleHttpPsr7Request;
$client= new Client();
$url="https://test.com?imei=123456789";
$request= new Request("GET", $url);

$promise = $client->sendAsync($request)->detach();

$promise->then(function ($response) {
    echo 'I completed! ' . $response->getBody();
});

//$promise->wait();

echo "Continuing with other code...n";
die;

My composer.json

{
    "name": "findy/findy",
    "description": "A brief description of your project",
    "require": {
        "guzzlehttp/guzzle": "^7.8"
    },
    "autoload": {
        "psr-4": {
            "GuzzleHttp\": "vendor/guzzlehttp/guzzle/src/"
        }
    },
    "minimum-stability": "stable"
}

When I run the code I get this error

Fatal error: Uncaught Error: Call to undefined method GuzzleHttpPromisePromise::detach()

Please help me