Scheduled refresh for Sharepoint files

I have created a report wherein I have two excel files from a sharepoint folder and combined them. I have used organizational credentials while entering the details for source settings in the desktop app.

I need help with how to add it a gateway and schedule a refresh for this. I tried "Sharepoint" and "Web" in the Data Source and authentication as Windows but it is not working. Everytime it throws an error - Invalid Credentials.

Please help.