Connect to Power BI Report Server or Report Server 2016 from iOS Power BI App

Hi,

I have VPN software on my phone.  I am able to activate and then browse to my report servers and see reports after entering windows credentials.  However, the reports don't render the phone layouts.  I've read I need to use Power BI app to see phone layout.  When attempting to add the report server - either 2016 or Power BI, I get an error:

Server address isn't valid:  
The certificate for this server is invalid.  
You might be connecting to a server that is prentending to be "reportserver.domain.com" 
which could put your confidential information at risk. 
Verify the address is a SQL Server Reporting Services address and try again. 

Can anyone tell me what the issue might be?  I'm suspecting I need the root server certificate for my organization or something similar on my device.

Thanks,

Sam