I have an external api which takes json body as payload. I am trying to send multiple parallel requests. So I am not using wp_remote_post()

The wp_remote_post() version of my code works perfectly.

Sending JSON payload using wp_remote_post()

This works!

        $response = wp_remote_post($url, [
            'body' = json_encode($registrants), // requried keys [firstName, lastName, email]
            'headers' = [
                'Authorization' = 'Bearer ' . $accessToken,
                'Content-Type' = 'application/json; charset=utf-8'
            ],
            'data_format' = 'body',
            'timeout' = 10,
        ]);

        return json_decode(wp_remote_retrieve_body($response));

Now I am trying to do the same with Request::request_multiple() But data isn't sending as json body.

Sending JSON payload using Request::request_multiple()

Does not work!

    $requests[] = [
            'url' = $url,
            'type' = 'POST',
            'body' = json_encode($registrant), // requried keys [firstName, lastName, email]
            'headers' = [
                'Authorization' = 'Bearer ' . $accessToken,
                'Content-Type' = 'application/json; charset=utf-8'
            ],
            'data_format' = 'body',
            'timeout' = 30,
        ];

    $options = [
        'data_format' = 'body'
    ];

    $resp = Requests::request_multiple($requests, $options);
    foreach($resp as $response){
        var_dump($response);
        $responses[] = json_decode($response-body);
    }

The error I am getting from API is very specific and throws when it doesn't get JSON body payload.