public function index(Request $request)
    {
        $clientId = 'ec905d7a-1e1c-40de-9c2c-7ca04c6992a1';
        $clientSecret = '9cdsXtFkJ.V._scS9vQ4_bH.9sn1BOjuL-';
        $signingKeyId = 'dc140fa4-d446-4fe8-b7ac-7877a3176c97';
        $signingKeyString = 'SnltUGMvd0gyejg5MHc3dkZUS2RYUGFjL1c3NjFqRmVRU2tVNTNiTGxmaz0=';

        $requestToken = Http::withHeaders([
                'Accept' => 'application/json',
                'Content-Type' => 'application/x-www-form-urlencoded',
                'api-version' => '0.12',
            ])->asForm()->post('https://sandbox.api.payme.hsbc.com.hk/oauth2/token', [
                'client_id' => $clientId,
                'client_secret' => $clientSecret
            ]);

        $accessToken = $requestToken->object()->accessToken;

        $traceId = '46860f3b-6ce0-4063-b7ba-3ad14b209773';
        $requestDateTime = date(DATE_RFC3339);
        $digest = 'SHA-256=gyT+LdIhNQLw2TjPTWRCWwIExmkRAoC2RvRM6FCggD4='; //calculate the SHA-256 hash of {"totalAmount":100.0,"currencyCode":"HKD"}
        $apiVersion = '0.12';

        $signatureString = "(request-target): post /payments/paymentrequests
api-version: $apiVersion
request-date-time: $requestDateTime
content-type: application/json
digest: $digest
accept: application/json
trace-id: $traceId
authorization: Bearer $accessToken";
        $signatureString = trim($signatureString);

        $signature = base64_encode(hash_hmac('sha256', $signatureString, base64_decode($signingKeyString), true));

        $response = Http::withHeaders([
            'Api-Version' => $apiVersion,
            'Request-Date-Time' => $requestDateTime,
            'Content-Type' => 'application/json',
            'Digest' => "Digest: $digest",
            'Accept' => 'application/json',
            'Trace-Id' => $traceId,
            'Signature' => 'Signature: keyId="'.$signingKeyId.'",algorithm="hmac-sha256",headers="(request-target) Api-Version Request-Date-Time Content-Type Digest Accept Trace-Id Authorization",signature="'.$signature.'"',
            'Authorization' => "Bearer $accessToken"
        ])->post('https://sandbox.api.payme.hsbc.com.hk/payments/paymentrequests', [
            'totalAmount' => 100.0,
            'currencyCode' => 'HKD',
        ]);

        print_r($response->body());die;
    }