Hi @ComputerHabit
Are trying to assign users to one specific collection ?
Have you configure the following ? Remote Desktop Services > Overview , under Properties, click Tasks > Edit properties
Or you may use Group Policy to specify the default connection:
Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Connection Client, specify the RDS collection that users should connect to by configuring the "Set default connection URL" policy setting. Then link this GPO to a OU