Cannot Connect to a PowerPivot Data Source from Report Server

Hi, I am trying to move from SharePoint Integrated mode to PBI Report Server. What used to work: - SharePoint with PowerPivot installed - Upload an Excel with PowerPivot data model to SharePoint - Create a SSRS report, indicate the data source as the Excel uploaded to SharePoint (e.g. Data Source="http://sharepoint/mydata.xlsx"). - In Report Builder, I can access the data including the DAX measures etc. What I am trying to do: - Set up Power BI Report Server - Set up Office Online Server (OOS) with Power Pivot configured - Upload the same Excel file to PBI RS - Connect the SSRS report to the PowerPivot file (e.g. Data Source="http://myReportServer/reports/excel/mydata.xlsx") - 404 file not found error I am able to view the Excel file directly in PBI RS with Excel Online configured but just cannot connect to the PowerPivot data model from SSRS. Thanks.