Using a REST API as a data source - Web.Contents Content option connecting anonymously

Hi,

I have another post on the community, which has been partially answered, but not resolved.

http://community.powerbi.com/t5/Integrations-with-Files-and/M-Query-to-use-POST-method-on-a-Web-API/m-p/115354#M7774

I have a Web data source connecting to the Sage One API. Im using a POST method.

I have tested the URL, headers, content-type and content on Postman.

And they work fine.

When trying to connect via Power BI Desktop I get this error:

DataSource.Error: Web.Contents with the Content option is only supported when connecting anonymously.
Details:
    DataSourceKind=Web
    DataSourcePath=https://accounting.sageone.co.za/api/1.1.2/AccountBalance/Get

This is the code I'm using, I have tried with authorisation in the header and setting it separately in the poppup and data source settings:

let
body=
"{
  ""FromDate"": ""2017-01-01"",
  ""ToDate"": ""2018-01-01""
}",
url = "https://accounting.sageone.co.za/api/1.1.2/AccountBalance/Get?ApiKey={GUIDGUID}&CompanyId=123456",

Source = Json.Document(Web.Contents(url, [ Headers = [#"Content-Type"="application/json"], Content = body] ))
in Source

I have seen a few posts relating to this error but none with a solution that would work for this scenario.

Can you check this isnt a Power BI bug...

Thanks

Digiroo