Creating a custom connection to Power BI using M via Visual Studios

Hello, 

I am attempting to create my first custom connection from an external electronic health program (using OAuth2) to power bi for visualization. The authorization process is complicated where I have to request and exchange a token each time it is accessed. 

My end goal is to login to power bi, choose the custom connector and create a dashboard. 

I have been unable to get my code to work. Visual Studios lists 0 errors, but when I run it I get the message " 0 arguments were passed to a function which expects 1". 

I would like help clearing the error and any advice anyone can provide is appreciated. (full code is included below)

section Chrono;

Profile="AAAA";
Client_ID="XXXX";
Client_Secret="YYY";
redirect_uri="https://oauth.powerbi.com/views/oauthredirect.html";
token_uri="https://drchrono.com/o/token";
authorize_uri="https://drchrono.com/o/authorize";
logout_uri="https://loginmicrosoftonline.com/logout.srf";
scope="patients:summary:read";
error_description="Error authorizing application";


//Login modal window dimensions

windowWidth=720;
windowHeight=1024;

[DataSource.Kind="Chrono", Publish="Chrono.Publish"]
shared Chrono.Contents=(url as text) =>
    let
        source=Json.Document(Web.Contents("https://drchrono.com"))

    in
        source;

//Data source kind description

Chrono=[
    TestConnection=(dataSourcePath)=>{"Chrono.Contents",dataSourcePath},
    Authentication=[
        OAuth=[
         StartLogin=StartLogin,
         FinishLogin=FinishLogin,
         Refresh=Refresh,
         Logout=Logout
        ]
    ],
    Label=Extension.LoadString("DataSourceLabel")
];

//Helper functions for OAuth2

StartLogin=(resourceUrl,state,display)=>
    let
        authorizeUrl=authorize_uri & "?" & Uri.BuildQueryString([
            response_type="code",
            client_id=Client_ID,
            redirect_uri=redirect_uri,
            state=state, 
            scope="patients:summary:read"
        ])
    in 
        [
            LoginUri=authorizeUrl,
            CallbackUri=redirect_uri,
            WindowHeight=720,
            WindowWidth=1024,
            Context=null 
        ];

FinishLogin=(context,CallbackUri,state)=>
    let
        //parse the full callback Uri and extract the Query String
        parts=Uri.Parts(CallbackUri)[Query],
        //if the query contains an "error" field, raise an error
        //otherwise call TokenMethod to exchange code for an access_token
        result=if(Record.HasFields(parts,{"error","error_description"})) then
            error Error.Record(parts[error],"Error authorizing application:" & "s'" & [error],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;

GetChronoData = (ChronoId as text)=>
    let
        //https://drchrono.com/o/authorize/?redirect_uri=REDIRECT_URI_ENCODED&response_type=code&client_id=CLIENT_ID_ENCODED&scope=SCOPES_ENCODED

        queryString=[
            client_id = Client_ID,
            scope = "patients:summary:read",
            format = "json",
            redirect_uri = "https://oauth.powerbi.com/views/oauthredirect.html",
            code="GET",
            response_type=":/api/patients_summary"
        ],
        source=Table.FromRows(Json.FromValue(Web.Contents("https://drchrono.com/o/authorize/?redirect_uri=REDIRECT_URI_ENCODED&response_type=code&client_id=CLIENT_ID_ENCODED&scope=SCOPES_ENCODED",[Query=queryString])))
    in
        source;
        

GetChronoId = (profile as text)=>
    let 
        source=Table.FromRows(Json.FromValue(Web.Contents("https://drchrono.com/o/authorize"))),
        first=Table.FirstValue(source)
    in
        first;

GetResponse = (client_id as text)=>
    let
        //https://drchrono.com/o/token/

        queryString=[
            refresh_token="get_refresh_token()",
            grant_type= "refresh_token", 
            client_id="XXXX",
            client_secret="YYYY"
        ],
        source=Table.FromRows(Json.FromValue(Web.Contents("https://drchrono.com/o/token/",[Query=queryString])))
    in
        source; 

// Token method from Dr.Chrono "https://drchrono.com/o/token"

TokenMethod=(grantType,tokenField,code)=>
    let
        queryString=[
            code="refresh_token",
            grant_type="refresh_token",
            redirect_uri="https://oauth.powerbi.com/views/oauthredirect.html",
            client_id="XXXXX",
            client_secret="YYY",
            access_token="access_token",
            refresh_token="refresh_token"
        ],
        tokenResponse=Web.Contents("https://drchrono.com/o/token",[Query=queryString])
    in 
        tokenResponse;


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

Chrono.Icons = [
    Icon16 = { Extension.Contents("Chrono16.png"), Extension.Contents("Chrono20.png"), Extension.Contents("Chrono24.png"), Extension.Contents("Chrono32.png") },
    Icon32 = { Extension.Contents("Chrono32.png"), Extension.Contents("Chrono40.png"), Extension.Contents("Chrono48.png"), Extension.Contents("Chrono64.png") }
];

Thank you, 

KT