Have Netskope configured with Microsoft Entra and SKIM provisioning.  I deploy the client via intune.
I want some 3rd party users to use Netskope to access some onprem applications.
We create them an account in entra bob@acme.com since they don't need email they don't specify an email address.
I can manually install the client but it fails when trying to register.  
Any thoughts? I don't want to waste a full office 365 license just to provide an email address.  I can put bob@hiscompany.com as an email address but that doesn't work. Does the email need to match the upn?