@rochemike
I had the same issue as you did.

To get around this error.
"│ Error: jsonrpc2: code 10 message: invalid parameters: {"errors":[{"instancePath":"/VIFs/0/mac","schemaPath":"#/properties/VIFs/items/properties/mac/minLength","keyword":"minLength","params":{"limit":1},"message":"must NOT have fewer than 1 characters"}]}
│
│ with xenorchestra_vm.rbbmspcs2,
│ on vm-windows.tf line 19, in resource "xenorchestra_vm""rbbmspcs2":
│ 19: resource "xenorchestra_vm""rbbmspcs2" {"

I modified the tf file to pass a mac_address

network {
  network_id = data.xenorchestra_network.cladevops01net1.id
  mac_address = be:d0:74:96:5a:66
}

It would then go and create the VM but once created. I'd log into XO, delete the VIF and readd it to get the randomized MAC address.

Please note that I also tried mac_address = null and mac_address = random which also failed.

Hope it helps.