Flutter http post request gives status code 401 - flutter

Question

I am using API to verify phone number provided by user.... on postman api give perfect response and give OTP code in response but in flutter status code 401 is returned
here is my code
Future verifyPhone(String phoneNumber) async {
try {
String token = "528724967b62c6c9e546aeaee1b57e234991ad98";
var body = <String, String>{};
body['user_number'] = phoneNumber;
var url = Uri.parse(ApiKeys.phoneVerifyApiKey);
var response = await http.post(
url,
headers: {
"Content-Type": "application/x-www-form-urlencoded",
"authentication": "Bearer $token"
},
body: body,
);
if (response.statusCode == 200) {
print("Code sent");
} else {
print("Failed to send code");
print(response.statusCode);
}
} catch (err) {
print(err.toString());
}
notifyListeners();
}
instead of "code sent" i get "failed to send code" and status code 401

Answer 1

EDIT
You can send form request this way
Future verifyPhone(String phoneNumber) async {
try {
String token = "528724967b62c6c9e546aeaee1b57e234991ad98";
var body = <String, String>{};
body['user_number'] = phoneNumber;
var url = Uri.parse(ApiKeys.phoneVerifyApiKey);
var headers ={
"Content-Type": "application/x-www-form-urlencoded",
"authentication": "Bearer $token"
};
var request = http.MultipartRequest('POST', url)
..headers.addAll(headers)
..fields.addAll(body);
http.StreamedResponse response = await request.send();
if (response.statusCode == 200) {
print("Code sent");
} else {
print("Failed to send code");
print(response.statusCode);
}
} catch (err) {
print(err.toString());
}
notifyListeners();
}
EDIT
To access :
var _data = jsonDecode(response);
var list = _data["data"];
print(list[0]['otp_code']);