Custom Connector Oauth2

Hi Team,

We've Smile CDR fhir server that supports oauth2. We're trying to connect to it using power bi, for this we're creating custom connector. We've added power bi as a client in Smile CDR. In the code we're passing every details however, we're getting 404 error. I've shared the code and screenshots below. 

Code:

// This file contains your Data Connector logic
section SmileCDR;

[DataSource.Kind="SmileCDR", Publish="SmileCDR.Publish"]
shared SmileCDR.Contents = (optional message as text) =>
let
_message = if (message <> null) then message else "(no message)",
a = "Hello from SmileCDR: " & _message
in
a;

// Data Source Kind description
SmileCDR = [
Authentication = [
OAuth = [
StartLogin = StartLogin,
FinishLogin = FinishLogin
]
],
Label = Extension.LoadString("DataSourceLabel")
];

StartLogin = (resourceUrl, state, display) =>
let
AuthorizeUrl = "http://xx.xx.xx.xx/issuer/oauth/authorize" & Uri.BuildQueryString([
client_id = "client_id",
scope = "scope",
state = state,
redirect_uri = " https://oauth.powerbi.com/views/oauthredirect.html"])
in
[
LoginUri = "http://xx.xx.xx.xx/issuer/oauth/authorize",
CallbackUri = " https://oauth.powerbi.com/views/oauthredirect.html",
WindowHeight = 800,
WindowWidth = 800,
Context = null
];

FinishLogin = (context, callbackUri, state) =>
let
Parts = Uri.Parts(callbackUri)[Query]
in
TokenMethod(Parts[code]);

TokenMethod = (code) =>
let
Response = Web.Contents("http://xx.xx.xx.xx/issuer/oauth/token", [
Content = Text.ToBinary(Uri.BuildQueryString([
client_id = "client_id",
client_secret = "client_secret",
code = code,
redirect_uri = " https://oauth.powerbi.com/views/oauthredirect.html"])),
Headers=[#"Content-type" = "application/x-www-form-urlencoded",#"Accept" = "application/json"]]),
Parts = Json.Document(Response)
in
Parts;

// Data Source UI publishing description
SmileCDR.Publish = [
Beta = true,
Category = "Other",
ButtonText = { Extension.LoadString("ButtonTitle"), Extension.LoadString("ButtonHelp") },
LearnMoreUrl = "https://powerbi.microsoft.com/",
SourceImage = SmileCDR.Icons,
SourceTypeImage = SmileCDR.Icons
];

SmileCDR.Icons = [
Icon16 = { Extension.Contents("SmileCDR16.png"), Extension.Contents("SmileCDR20.png"), Extension.Contents("SmileCDR24.png"), Extension.Contents("SmileCDR32.png") },
Icon32 = { Extension.Contents("SmileCDR32.png"), Extension.Contents("SmileCDR40.png"), Extension.Contents("SmileCDR48.png"), Extension.Contents("SmileCDR64.png") }
];

After running the code we're able to reach to signin page of Smile CDR. On sign in page we're passing the credentials and then we're getting 404 error as displayed in the screenshot. 

Could anyone provide any suggestions?

1st2nd3rd