Using Guzzle to retrieve API via (POST), unable to pass JSON parameters for query

I have created an API request, it connects to the server fine and passes basic authentication. The error I receive is

“Uncaught GuzzleHttpExceptionClientException: Client error: POST http://my.api.com/dest/addr resulted in a 400 Bad Request response: {“code”:400,”result”:”Missing customer id”

I have tried many ways to pass the query parameters and none of them have worked. I checked to make sure the JSON being output was formatted correctly. I have followed the directions in the Guzzle documentation. I have also tried every solution I could find in the forums and none of them gave me a different response. I am not sure what I am missing, hoping someone can see what the problem might be… I have pasted what I feel is the code that best follows the Guzzle documentation below. Thanks.

    <?php
    require __DIR__.'/../vendor/autoload.php';
    use GuzzleHttpClient;
    use GuzzleHttpExceptionRequestException;
    Use GuzzleHttpPsr7;

    try {

        $client = new Client(['base_uri' => 'http://my.api.com/']);
        $credentials = base64_encode('12345');

        $request_param = [
            'json' => [
                'customer' => [
                    'name' => 'Mary',
                    'id' => 111
                ],
                'products' => [
                    [
                        'product_id' => 2,
                        'qty' => 3
                    ]
                ]
            ]
        ];
        $request_data = json_encode($request_param, true);

        $headers = ['headers' => [
            'Content-Type' => 'application/json',
            'Authorization' => 'Basic ' . $credentials
        ]];

        $response = $client->request('POST', 'dest/addr', $headers, $request_data);

        echo $response->getStatusCode();
        echo "<br />";
        echo $response->getHeader('content-type')[0];
        echo "<br />";
        echo "<pre />";
        echo $response->getBody()->getContents();
    }
    catch(GuzzleHttpExceptionClientException $e) {
        echo $e->getCode(). '<hr />';
        echo $e->getMessage();
    }
        //Server Exception
    catch(GuzzleHttpExceptionServerException $e) {
        echo $e->getCode(). '<hr />';
        echo $e->getMessage();
    }

Answer

if your my.api.com can accept json request(not form params json=json_string&something=value in post body).you could try like this

$json_data = [
    'customer' => [
        'name' => 'Mary',
        'id' => 111
    ],
    'products' => [
        [
            'product_id' => 2,
            'qty' => 3
        ]
    ]
];
$headers = [
    'Authorization' => 'Basic ' . $credentials
];

$response = $client->request('POST', 'dest/addr', [
    'json' => $json_data,
    'headers' => $headers
]);