Web.Contents failed to get contents | (429): Data API call already in progress

Well v-lid-msft, that'll be happening in parallel. 

For now I had a closer look at the Web.Contents ManualStatusHandling option and think it should work to implement the wait-retry pattern for the 429 error. But saying that, I implemented it and get an error I cannot figure out.

I followed https://docs.microsoft.com/en-us/power-query/waitretry#putting-it-all-together but now getting the error message:

"Expression.Error: The import Value.WaitFor matches no exports. Did you miss a module reference?". 

My code for the query: 

let
Source = Csv.Document(
    let
        waitForResult = Value.WaitFor((iteration) =>
                    let
                        result = Web.Contents("https://au...censored...com",[RelativePath="/api/v1/surveys/selfserve/...censored.../data?fields=uuid,age,gender,...censored...", 
                            Headers=[#"x-apikey"="...censored..."],ManualStatusHandling={429}]),
                        buffered = Binary.Buffer(result),
                        status = Value.Metadata(result)[Response.Status],
                        actualResult = if status = 429 then null else buffered                    
                    in
                        actualResult,
                (iteration) => #duration(0,0,0,Number.Power(2, iteration)), 5)
    in
        waitForResult,
            [Delimiter="	", Encoding=1252, QuoteStyle=QuoteStyle.None]),    
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true])
in
    #"Promoted Headers"

Any idea what I might be doing wrong and how to fix it?