OAuth 2.0 ROPC issue(Data Connector)

Hi 

I have created a data connectors that uses an Oauth 2.0 flow to connect to our cloud environment. I have used the client_id, username and password in the flow, yet while execution it prompts for sign credentials which shouldn't be the case. Based on the document this is a special error when there is something wrong with the data source kind and path. 

[DataSource.Kind = "System" , Publish="System.Publish"]
shared System.Contents = Value.ReplaceType(SystemNavTable, type function (url as Uri.Type) as any);

// Oauth Data Source Kind description

System = [
Testconnection = (dataSourcePath) => {"System.Contents"},
Authentication = [
OAuth = [
StartLogin=StartLogin,
FinishLogin=FinishLogin,
Refresh=Refresh,
Logout=Logout
]
],
Label = "System Connector"
];

StartLogin = (resourceUrl, state, display) =>
let
authorizeUrl = authorize_uri & "?" & Uri.BuildQueryString([
client_id = client_id,
redirect_uri = redirect_uri,
state = state,
scope = "offline_access " & GetScopeString(scopes, scope_prefix),
response_type = "code",
response_mode = "query",
login = "login"
])
in
[
LoginUri = authorizeUrl,
CallbackUri = redirect_uri,
WindowHeight = 720,
WindowWidth = 1024,
Context = null
];

FinishLogin = (context, callbackUri, state) => //FinishLogin = (context, CallbackUri, state) =>
let
// parse the full callbackUri, and extract the Query string
parts = Uri.Parts(callbackUri)[Query],
// if the query string contains an "error" field, raise an error
// otherwise call TokenMethod to exchange our code for an access_token
result = if (Record.HasFields(parts, {"error", "error_description"})) then
error Error.Record(parts[error], parts[error_description], parts)
else
TokenMethod("authorization_code", "code", parts[code])
in
result;

Refresh = (resourceUrl, refresh_token) => TokenMethod("refresh_token", "refresh_token", refresh_token);

Logout = (token) => logout_uri;

//This is called when StartLogin() is completed and a redirect occurs.
TokenMethod = (grantType, tokenField, code) =>
let
queryString = [
client_id= "passing the client id value",
scope="openid clientid(value) offline_access",
grant_type="password",
//response_type="token",
username="passing the username value",
password="passing the password value!"
],
queryWithCode = Record.AddField(queryString, tokenField, code),

tokenResponse = Web.Contents(token_uri, [
Content = Text.ToBinary(Uri.BuildQueryString(queryWithCode)),
Headers = [
#"Content-type" = "application/x-www-form-urlencoded",
#"Accept" = "application/json"
],
ManualStatusHandling = {400}
]),
body = Json.Document(tokenResponse),
result = if (Record.HasFields(body, {"error", "error_description"})) then
error Error.Record(body[error], body[error_description], body)
else
body
in
result;

As you see, I'm passing the username and password but it still redirects me to the login screen(which again according the microsoft doc is an error). Can someone please advise what is wrong with the above code.