400 bad request in storefront api with flutter with http request

Retired Boards Appdev Custom Storefronts
,
1 
 try {
      var uri = Uri.parse("https://nextsavy-demo.myshopify.com/api/2023-07/graphql.json");
      var response = await http
          .post(uri, body: {"query": "{
  "query": "query GetCart($cartId: ID!) { cart(id: $cartId) { id lines(first: 10) { edges { node { id quantity } } } cost { totalAmount { amount currencyCode } subtotalAmount { amount currencyCode } totalTaxAmount { amount currencyCode } totalDutyAmount { amount currencyCode } } buyerIdentity { email phone customer { id } countryCode deliveryAddressPreferences { ... on MailingAddress { address1 address2 city provinceCode countryCodeV2 zip } } } } }",
  "operationName": "GetCart",
  "variables": {
    "cartId": "gid://shopify/Cart/c1-007280228acabc5803619ad*********"
  }
}"}, headers: {
    "Content-Type": "application/json; charset=UTF-8",
    "X-Shopify-Storefront-Access-Token": token
  })
          .timeout(const Duration(seconds: timeOutDuration));
      print(response.statusCode);
      if (response.statusCode >= 200 && response.statusCode < 300) {
        return response.body;
      } else {
        _handleResponse(response);
      }
    } on SocketException {
      throw FetchDataException('No internet connection');
    } on TimeoutException {
      throw ApiNotRespondingException('Api not responding');
    }

i use http package in flutter for make api request for getting cart using store front api with graphQl.
i pass query in body parameter.
this is work well in postman and get response. but when i implement in my flutter app it dosen’t work.
i got response “Bad request , error code 400”,