How to instantiate GuzzleRequest?

I am new at php/symphony/laravel and i working on a project. For that projet, i’m trying to configure an API.
I don’t know how i can instantiate a GuzzleRequest to post data and generate authorization header for the API.
This is the GuzzleRequest created

  $request = new GuzzleRequest(
            method: 'POST',
            uri: $url,
            //body:null,
        );

Inside the GuzzleRequest that i’ve instantiate, i want to pass data inside the body parameters.
The body parameters can take : string|resources|null|StreamInterface but this data i want to pass :

{
    "payItemId": "S-112-948-MTNMOMO-20052-200040001-1",
    "amount": 1000
}

This the full function code :

function headerauthorization()
    {

        $token = "716c3fcf-98bd-435e-a16d-befc3b96da35";
        $secret = "9f96a7ed-338f-4609-83f8-27ce60fe87f4";
        //$url = "https://s3p.smobilpay.staging.maviance.info/v2/cashin?serviceid=20052";
        $url = "https://s3p.smobilpay.staging.maviance.info/v2/quotestd";

        $config = new \Maviance\S3PApiClient\Configuration();
        $config->setHost($url);
        $client = new \Maviance\S3PApiClient\ApiClient($token, $secret, ['verify' => false]);


        $request = new GuzzleRequest(
            method: 'POST',
            uri: $url,
            //body:null, 
        );

        $curl = curl_init();
        curl_setopt_array(
            $curl,
            array(
                CURLOPT_URL => 'https://s3p.smobilpay.staging.maviance.info/v2/quotestd',
                CURLOPT_RETURNTRANSFER => true,
                CURLOPT_ENCODING => '',
                CURLOPT_MAXREDIRS => 10,
                CURLOPT_TIMEOUT => 0,
                CURLOPT_FOLLOWLOCATION => true,
                CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
                CURLOPT_CUSTOMREQUEST => 'POST',
                CURLOPT_HTTPHEADER => array(
                    'Authorization:' . $client->buildAuthorizationHeader($request) . ''
                ),
            )
        );
        $response = curl_exec($curl);
        curl_close($curl);
        $response = json_decode($response, true);

    }

Why do i use GuzzleRequest ? Because the function buildAuthorizationHeader($request) only takes RequestInterface type as parameters. i firstly tried the following code(the method is GET and there’s no body’s parameters) for the first Api request and it works fine for me. But now i have a Post method and a body parameters to insert.

This is the first code which works fine for me

 function headerauthorization()
    {

        $token = "716c3fcf-98bd-435e-a16d-befc3b96da35";
        $secret = "9f96a7ed-338f-4609-83f8-27ce60fe87f4";
        $url = "https://s3p.smobilpay.staging.maviance.info/v2/cashin?serviceid=20052";
       

        $config = new \Maviance\S3PApiClient\Configuration();
        $config->setHost($url);
        $client = new \Maviance\S3PApiClient\ApiClient($token, $secret, ['verify' => false]);
        
        
        $request = new GuzzleRequest(
            method: 'GET',
            uri: $url,
            // headers: [],
            // body: null,
        );   
        $curl = curl_init();
        curl_setopt_array($curl, array(
           CURLOPT_URL => 'https://s3p.smobilpay.staging.maviance.info/v2/cashin?serviceid=20052',
           CURLOPT_RETURNTRANSFER => true,
           CURLOPT_ENCODING => '',
           CURLOPT_MAXREDIRS => 10,
           CURLOPT_TIMEOUT => 0,
           CURLOPT_FOLLOWLOCATION => true,
           CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
           CURLOPT_CUSTOMREQUEST => 'GET',
           CURLOPT_HTTPHEADER => array(
                'Authorization:'.$client->buildAuthorizationHeader($request).''
            ),
        )
        );
        $response = curl_exec($curl);
        curl_close($curl);
        $response = json_decode($response, true);
        $payItemId = $response[0]["payItemId"];
       
    } 

>Solution :

Set the body-data in an array and then json_encode like this.

$body = json_encode([
    "payItemId" => "S-112-948-MTNMOMO-20052-200040001-1",
    "amount" => 1000,
]);

Then add another field just after the CURLOPT_CUSTOMREQUEST => 'POST', like this

CURLOPT_POSTFIELDS => $body,

Finally set the CURLOPT_HTTPHEADER as

CURLOPT_HTTPHEADER => array(
            'Content-Type: application/json',
            'Authorization: ' . $client->buildAuthorizationHeader($request)
        ),

Try this it will work.