Security - share only certain Rows AND certain Tabs with users

mmace1 

This problem...

Copied the report to a new workspace, removed the unwanted tabs, filtered data down (just via the interface, no row level security) to what was wanted. Publish app, give access to external users:

Problem: Error message about them needing permissions to the underling datasets.

 is caused by the target users not having "Read" permission to the source dataset.  Once they've been provided this permission (in the dataset- "manage permissions" menu) - they will be able to see the app that you just created.  Savvy users may figure out how to 'undo' the filters you set with the interface - but if you hide the slicer from view using the selection pane - you can maybe avoid having to setup RLS.  

RLS is setup in the Power BI Desktop file - and if done correctly - you won't have the 'filter the data down' in the report canvas - because your security rules and roles will do that for you.  This will require a bit more work on your part to set up the file - but should have the desired effect.  

Either way - you'll still need to add the report viewers to a dataset permission role - in order for them to stop getting that error.  

"Error message about them needing permissions to the underling datasets."