'Add Existing User' option in User Management

I want to add a user to my account as a viewer. I am unable to do this because they have already been added as a user by another account.

It seems crazy that users are unable to be 'viewers' across multiple authoring accounts.

A real world situation that occurred:

We wanted a client to review our work securely, on the CenarioVR server, so they could access it on the CenarioVR App. This client owns their own license for CenarioVR and we will be transferring the scenario to them on completion, but before this, we are managing the review stage. I was unable to assign this client's (and their colleagues) email addresses as a new user because they were already registered as users on their own CenarioVR authoring account. In the end, we had to create a new 'demo' email and assign this as a user, giving them the login to this user.

Another example is that my work email address cannot be assigned as a user by other CenarioVR authoring accounts, so I am unable to review scenarios made by others on the CenarioVR server unless it is made Public (where is MUST be private).

Thanks,

Jack