Subinterfaces error when adding into virtual router

Describe the bug

When adding a subinterface to Router, i get this error:

panos_panorama_virtual_router.overlay[1]: Creating...
panos_panorama_virtual_router.overlay[0]: Modifying... [id=gwlb-emfmc-eu-west-1a::vsys1:overlay]
panos_panorama_virtual_router.overlay[0]: Modifications complete after 2s [id=gwlb-emfmc-eu-west-1a::vsys1:overlay]

Error:  overlay -> interface is invalid

  on panorama.tf line 93, in resource "panos_panorama_virtual_router" "overlay":
  93: resource "panos_panorama_virtual_router" "overlay" {

Expected behavior

Should add the SubInterface and complete.

Current behavior

The SubInterface seems to be added in the config, but the TF Plan stops.

Possible solution

🤷🏻‍♂️

Steps to reproduce

resource "panos_panorama_virtual_router" "overlay" {
  count    = var.no_of_zones
  name     = "overlay"
  template = panos_panorama_template.this[count.index].name
  interfaces = [
    panos_panorama_ethernet_interface.ethernet1_1[count.index].name,
    panos_panorama_ethernet_interface.ethernet1_2[count.index].name,
//    panos_panorama_layer3_subinterface.ethernet1_2_1[count.index].name,
// TODO - Fix this hard coded reference
    "ethernet1/2.1"
  ]
}

Screenshots

Context

Trying to create Subinterfaces for assignment to AWS GWLB Endpoints

Your Environment

Version used:

Terraform v0.14.3

provider registry.terraform.io/hashicorp/aws v3.42.0
provider registry.terraform.io/hashicorp/azurerm v2.60.0
provider registry.terraform.io/hashicorp/http v2.1.0
provider registry.terraform.io/hashicorp/random v3.1.0
provider registry.terraform.io/paloaltonetworks/panos v1.8.3

Your version of Terraform is out of date! The latest version is 0.15.4. You can update by downloading from https://www.terraform.io/downloads.html

PaloAltoNetworks / terraform-provider-panos

Subinterfaces error when adding into virtual router #285