dataflows and functions

Hi, 

I am attempting migrate some of my PBI Desktop queries to Dataflows in the BI Service.

Some of these queries reference a function, The function accepts an argument of a URL - this URL is then used to extract all the items in a particular list on that project site.  However when the function is referenced in the query it is asking for credentials.  When I attempt to enter credentials via an organisational account the option to sign is is greyed out even though the dialog suggests I am not signed in.  Any ideas?

Function code:

let
LoadList = (site as text) =>
let 
Source = OData.Feed(site&"/_api/lists/getbytitle('Risks')/items")
in
Source
in
LoadList

Many thanks

Mick