Adding GroupUserAccessRight Member to PowerBI workspace

When I try to add a user with GroupUserAccessRight other then "Admin":

{
  "emailAddress": "[email protected]",
  "groupUserAccessRight": "Member"
}

the API is responding with an error.

I know there's "Note" on the doumentation's page that states: Note: Only Admin access right is supported. 

Source: https://docs.microsoft.com/en-us/rest/api/power-bi/groups/addgroupuser

When will the other GroupUserAccessRight be supported by the API?

Thanks in advance.

Ton Swart