Setting up VD - Create tenant

I'm following the white paper to setup Windows virtual desktop.

Every step goes fine until now.  This step blocks me in going further with the setup.

Add-RdsAccount -DeploymentUrl "https://rdbroker.wvd.microsoft.com"

If i use the global administrator account, i get the following error :

AADSTS50020: User account 'eric@mycompany.com' from identity provider 'live.com' does not exist in tenant 'MS Azure Cloud' and cannot access the application 'fa4345a4-a730-4230-84a8-7d9651b86739'(Windows Virtual Desktop Client) in that tenant. The account needs to be added as an external user in the tenant first. Sign out and sign in again with a different Azure Active Directory user account.

In reading different articles on the net, i found this to be an issue with many users. One guy said you need to make another external user als global administrator and run the command again, so i did.

But then i get this error :

Add-RdsAccount : Er zijn één of meer fouten opgetreden.
At line:1 char:1
+ Add-RdsAccount -DeploymentUrl "https://rdbroker.wvd.microsoft.com"
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Add-RdsAccount], AggregateException
    + FullyQualifiedErrorId : System.AggregateException,Microsoft.RDInfra.RDPowershell.Context.AddRdsAccount

So now i'm stuck at this point.

Any help would be welcome.