Attach host not define a new host

I have a host with IP x.y.z.w and following code:

resource "vsphere_distributed_virtual_switch" "majd_dvs" {
  datacenter_id =

  uplinks        = ["tfup1"]
  active_uplinks = ["tfup1"]

  host {
     host_system_id = "${}"
     //devices        = ["${var.network_interfaces}"]
     devices        = ["vmnic0","vmnic1"]

I get the following error:
Cannot complete a vsphere distributed switch operation for one or more
I have three question:

  1. what does mean above error?
  2. does host block in vsphere_distributed_virtual_switch resource define a new host or attach my host to DVS?
  3. How can I attach host to my DVS if my host is exist?