User Account from Identity Provider Does Not Exist In Tenant

Hi all,

I have a business who shares it's Power BI reports with Sales Reps who are all external to the business.  This has mostly been fine using external emails from a variety of tenants.  However today, one user couldn't log in with the following error. 

We did grant additional access to a new app last week however the user has confirmed they were able to log in after that day, and today they cannot.  

I've read information on providing access to Azure as described here.  The thing is - they could access this last week, so why now? Also we never did this before as it would require their head office to grant the access and we never went through that route.  

Looking for ideas (a) to resolve and (b) to understand how this may have come about. 

The user definitely has access to the App and Data, plus they've been assigned to the relevant RLS role.  They appear to to be able to log into the Power BI Tenant at all.

Thanks in advance.



Cheers

Kaycee