Paypal create order request gives me Unhandled Exception: DioException [bad response]: The request returned an invalid status code of 400. in flutter

Question

Here is my code let me know where i am going wrong i am generating order request using sandbox url for create order

 createOrder({accessToken})async{
    var headers = {
      'Content-Type': 'application/json',
      'PayPal-Request-Id': '7b92603e-77ed-4896-8e78-5dea2050476a',
      'Authorization': 'Bearer ${accessToken}',
    };
    var data = json.encode({
      "intent": "CAPTURE",
      "purchase_units": [
        {
          "items": [
            {
              "name": "T-Shirt",
              "description": "Green XL",
              "quantity": "1",
              "unit_amount": {
                "currency_code": "USD",
                "value": "${amount}"
              }
            }
          ],
          "amount": {
            "currency_code": "USD",
            "value": "${amount}",
            "breakdown": {
              "item_total": {
                "currency_code": "USD",
                "value": "${amount}"
              }
            }
          }
        }
      ],
      "application_context": {
        "return_url": "https://example.com/return",
        "cancel_url": "https://example.com/cancel"
      }
    });
    var dio = Dio();
    var response = await dio.request(
      'https://api-m.sandbox.paypal.com/v2/checkout/orders',
      options: Options(
        method: 'POST',
        headers: headers,
      ),
      data: data,
    );

    if (response.statusCode == 200) {
      showProgressDialog(false);
      print(json.encode(response.data));
      Map<String, dynamic> mapppedResponse = response.data;
      payId = mapppedResponse['id'];
      if (webViewController != null) {
        webViewController.loadUrl((mapppedResponse['links'] as List)[1]['href']);
      }
    }
    else {
      print(response.statusMessage);
      showProgressDialog(false);
    }
  }

How can i resolve this issue and from where i can get PayPal-Request-Id right now i am using dummy is this creating issue.

please do reply if you have any kind of info related to it