You plan to use existing virtual machines in an Azure Virtual Desktop deployment and have created a host pool. To add the existing VMs to the host pool, what must you do first?

To add existing virtual machines to an Azure Virtual Desktop host pool, you must first generate a registration key. This key is essential because it allows the Azure Virtual Desktop agent, which you install on each VM, to securely connect and register the VM with the specified host pool. Without a valid registration key, the agent cannot establish this connection, and the VM will not be recognized as a session host. Registering the Microsoft.DesktopVirtualization provider is a one-time subscription-level action, usually done before creating host pools, not specifically for adding VMs. The Invoke-AzVMRunCommand cmdlet can be used to execute scripts on VMs, but it's not the initial step for registration. Creating a role assignment is for granting permissions, not for registering session hosts.