Попробуйте это
http.Response response = await http.post("http://18.191.223.160/webservices/FoodSubCategoryList",
body: { "userid": "2",
"CUSTOMERID":"158",
"OFFSET":"0"},
headers: {
"Accept": "application/json",
"Tokenvalue": "sOzz0Y6O",
"Content-Type": "application/json"
});
var responseJson = json.decode(response.body);
вместо этого
var body = jsonEncode({
"userid": "2",
"CUSTOMERID":"158",
"OFFSET":"0"
});
final response = await http.post(
"http://18.191.223.160/webservices/FoodSubCategoryList",
headers: {
"Accept": "application/json",
"Tokenvalue": "sOzz0Y6O",
"Content-Type": "application/json"
}, body: body
);
Надеюсь, это поможет