Help!! - Having trouble adding a SharePoint Excel to an On-Premises Data Gateway

Hi,

I have a dedicated Server running On-Premises Data Gateway. Through logging on to that Server I can see the Data Gateway is installed and running.

I logon to the Power BI Service account (UserA) that will be used to add datasources to the Data Gateway. This is the same account that was signed into when configuring the Data Gateway on the dedicated Server. So the UserA Power BI Service account should see the configured Data Gateway available to add data sources against it - and I confirm I can see it.

I have an Excel file residing in a SharePoint location. I want to add that Excel file as a data source against the Data Gateway via the UserA Power BI Service account. When attempting this is is failing - why?  Below is the screenshot I receive notifying of the error (I've hidden the full details but it was only the SharePoint path). I've tried connecting to this Excel file in SharePoint using Datasource Type = 'File', 'SharePoint, and 'Web' but no joy on any of the attempts.

Two tests I have done to narrow down the issue:

1) When opening the .pbix file using the UserA account and clicking 'refresh', it does successfully refresh the data (of course I am prompted for to provide the UserA credentials). From this test, I know that UserA has permissions to the source data and it's locations.

2) In the UserA Power BI Service account I add a datasource to the Data Gateway. This datasource is an Excel file on the local drive. The datasource is added successfully. From this test, I know datasources be added to the Data Gateway using the UserA account.

With the two tests above having completed successfully then why is the failure I'm receiving happening?

Thanks in advance.