Http Post Headers are not working

I am trying to do a post request in Flutter

Below is the code

final String url = Urls.HOME_URL;
String p = 'Bearer $vAuthToken';

final Map tokenData = {
"Content-Type": "application/x-www-form-urlencoded",
'Vauthtoken': p
};

final Map data = {
'classId': '4',
'studentId': '5'
};

final response = await http.post(Uri.parse(url),
headers: tokenData,
body: jsonEncode(data),
encoding: Encoding.getByName("utf-8"));

if (response.statusCode == 200) {
print(response.body);
} else {
print(response.body);
}
However the header data is not working. I have the correct data and everything. This request works perfectly when done in Postman Client. Any one has any idea what is wrong? Any suggestion is appreciated.