Gateway grey out

Hi

I've found many threads on this, but I've yet to find a case specifically like mine.  I'd really like to be simply pointed at a thread I've missed :smileywink:

My PBIX file points at a SQL database and an Excel file stored in my company's O365 SharePoint.  My Organisation account (similar to my Windows account) gets me into SharePoint O365 etc.

On the desktop (PBIX) the data sources work perfectly.

However, when I publish my PBIX I can only see the SQL datasources:

When I try to add a SharePoint data source I get no Organization authentication option and my attempts to use Windows authentication fail.  I've tried my Windows username firstName lastName, email address [email protected], WINDOWSDOMAIN\firstName lastName, WINDOWSDOMAIN\firstName.lastName and even AzureAD\firstName lastName, AzureAD\firstName.lastName

Any thoughts?

Thanks very much.