Connecting to an API that uses OAuth with Power Query

Hi All,

I'm trying to ingest data from this API: https://api.nsw.gov.au/Product/Index/22

The site lets you test the endpoints in the browser and I get a valid response using the test credentials.

I'm able to get the access token in Power Query.  But the next request which uses the access token doesn't seem to work.  Power BI Desktop tells me the credentials used are not valid... 

M script below... any help would be much appreciated.

//https://api.nsw.gov.au/Product/Index/22
//Visit the site above and click on 'Sandbox and doc'
//This will present test credentials to try the endpoint

let
    testAPIKey = "1MYSRAx5yvqHUZc6VGtxix6oMA2qgfRT",
    testAPISecret = "BMvWacw15Et8uFGF",

    // Concatenates the test Key & Secret and converts to base64
    authKey = "Basic " & Binary.ToText(Text.ToBinary(testAPIKey & ":" & testAPISecret),0),

    url = "https://api.onegov.nsw.gov.au/oauth/client_credential/accesstoken",
    // Make a POST request to obtain a bearer token
    GetJson = Web.Contents(url,
        [
            Headers = 
                [
                #"Authorization"=authKey,
                #"Content-Type"="application/json"
                ],
            Content = Text.ToBinary("grant_type=client_credentials") 
        ]
    ),

    // Get the bearer token from the response
    AccessToken = Text.From(GetJson),

    GetJsonQuery = 
    Web.Contents("https://api.onegov.nsw.gov.au/FuelPriceCheck/v2/fuel/prices",
        [
        Headers=
            [
            #"Authorization"="Bearer " & AccessToken, 
            #"Content-Type"="application/json; charset=utf-8",
            #"apikey"=testAPIKey,
            #"Accept"="application/json",
            #"transactionid"="1",
            #"requesttimestamp"= DateTime.ToText(DateTime.LocalNow(), "dd/MM/yyyy hh:mm:ss tt")
            ]
        ]
    ),
    FormatAsJsonQuery = Json.Document(GetJsonQuery)
in
    FormatAsJsonQuery