I have gained a bit of  headway on this model. I now have Exel files being updated from on-premises systems via the Power BI gateway.  That is a great win!


The model is, however, a bit different than I was thinking and different then what I believe is represented in this article (last option in the list)  https://support.office.com/en-us/article/Use-external-data-in-workbooks-in-SharePoint-Online-8d7f5dc...


The end goal is: Open a web page in SharePoint with a Excel Web part and click refresh data and that data will refresh on demand from an on-premises data source.


While I can get the Excel file to refresh by setting it up in Power BI and refreshing from Power BI. I still can't get the "refresh data" button in Excel Online/Excel Services Online to work. Fails everytime. 


I have progressed quite a bit thanks to your help John. So thank you!