title: Can't schedule refresh in PowerBI Service
body: <p>I have a PowerBI report with 2 tables sourced from separate web API calls to a similar service, let's call it MyService.  The service returns json.  The report refreshes perfectly within PBI Desktop.  The report publishes to PowerBI.com where it runs without a hitch.  On-demand refresh of the report's dataset in the PBI Service works perfectly too.</p>
  
  <p><a href="https://i.stack.imgur.com/NGe0r.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/NGe0r.jpg" alt="Refresh History"></a></p>
  
  <p>I can't schedule a refresh for this report because the option is greyed out.  There is an error reported in the Data source credentials section where one of the two Web sources reports it cannot connect to MyService.  The error is... "Your data source can't be refreshed because the credentials are invalid. Please update your credentials and try again." </p>
  
  <p><a href="https://i.stack.imgur.com/hLEGZ.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/hLEGZ.jpg" alt="Data source credentials"></a></p>
  
  <p>Attempting to edit the credentials for the failing connection results in a 500 Internal Server Error.  </p>
  
  <p>This error is unexpected because I understood the on-demand refreshes &amp; scheduled refreshes would use the same data source(s).  There is no where to specify different data sources/credentials for on-demand vs. scheduled so I just assume they share the same sets of credentials.</p>
  
  <p>Is something weird going on or does my understanding of the innards of the PBI Service need realignment?</p>