I am getting error because of Block by CORS policy Error Flutter wev

I am using flutter to create a web application, I got this error while accessing the API I don’t know what is going wrong I am using .NET for backend which is connected with SAP for data. Can someone tell me how to fix this:-

Access to XMLHttpRequest at ‘API_URL’
from origin ‘http://localhost:64848’ has been blocked by CORS policy:
Response to preflight request doesn’t pass access control check:
No ‘Access-Control-Allow-Origin’ header is present on the requested resource.

Here is my code :-

await DioUtil.getInstance()
      .post(
    apiUrl,
    options: Options(
      headers: {'content-type': 'application/json', 'Access-Control-Allow-Origin': true, "Accept": "*/*"},
    ),
    data: body,
  )
      .then((value) {
    
      debugPrint("Status Code == " + value.statusCode.toString());
      
      } else {
        tryAgainDialog(getContractFullReport);
        setState(() {
          _isLoading = false;
        });
      }
    });
  });

I am using interceptor with basic auth for authorization to backend.