SharePoint Online List Data Source Connection error.

Hi,

I have report server 2016 and Power BI Desktop (Oct 2017) and I'm trying to create a data source that connects to a SharePoint list. It seems like it should be the simplest thing, we've already create Power BI dashboards fromSharePoint lists using Get Data from the ribbon. However, we need that data to be pulled from SharePoint adhering to the SharePoint security trimming, so we want to create a data source that will pull the data using the credentials of the user viewing the report.

(if any of this doesn't sound right, or we're taking the wrong approach, please say, we're fairly new to it)

Anyway, I'm trying to create my data source in Report Server > New > Data Source

Selecting "Connection Type" = Microsoft SharePoint List 

then the Connection String is

"data source=https://domain/site/subsite"

However, I am consistently getting the message telling me that this is not a valid connection string despite this article saying that's how the connection string should look.

I've tried this from Report Builder and had the same error and tried a number of variations on this connection string, so am I missing something obvious here or is there something else causing this.

Any help appreciated.

Thanks