The 'resourceTargetId' property of endpoint 'vm1-TF' is invalid or missing

Terraform
1

I want to implement traffic manager in Terraform between two vm’s from different locations (West Europe and North Europe). I attach my code, but I don’t know how to configure “target_resource_id” for each vm, because the vm’s were created in a for loop, also the networks. The traffic manager would switch to the secondary vm, in case of failure of the first vm. Any ideas?

My code:

variable "subscription_id" {}
variable "tenant_id" {}
variable "environment" {}
variable "azurerm_resource_group_name" {}
variable "locations" {
  type = map(string)
  default = {
    vm1 = "North Europe"
    vm2 = "West Europe"
  }
}

# Configure the Azure Provider
provider "azurerm" {
  subscription_id = var.subscription_id
  tenant_id       = var.tenant_id
  version = "=2.10.0"
  features {}
}

resource "azurerm_virtual_network" "main" {
  for_each            = var.locations
  name                = "${each.key}-network"
  address_space       = ["10.0.0.0/16"]
  location            = each.value
  resource_group_name = var.azurerm_resource_group_name
}

resource "azurerm_subnet" "internal" {
  for_each             = var.locations
  name                 = "${each.key}-subnet"
  resource_group_name  = var.azurerm_resource_group_name
  virtual_network_name = azurerm_virtual_network.main[each.key].name
  address_prefixes     = ["10.0.2.0/24"]
}

resource "azurerm_public_ip" "example" {
  for_each                = var.locations
  name                    = "${each.key}-pip"
  location                = each.value
  resource_group_name     = var.azurerm_resource_group_name
  allocation_method       = "Static"
  idle_timeout_in_minutes = 30

  tags = {
    environment = "dev01"
  }
}

resource "azurerm_network_interface" "main" {
  for_each            = var.locations
  name                = "${each.key}-nic"
  location            = each.value
  resource_group_name = var.azurerm_resource_group_name

  ip_configuration {
    name                          = "testconfiguration1"
    subnet_id                     = azurerm_subnet.internal[each.key].id
    private_ip_address_allocation = "Dynamic"
    public_ip_address_id          = azurerm_public_ip.example[each.key].id
  }
}

resource "random_password" "password" {
  length = 16
  special = true
  override_special = "_%@"
}

resource "azurerm_virtual_machine" "main" {
  for_each              = var.locations
  name                  = "${each.key}t-vm"
  location              = each.value
  resource_group_name   = var.azurerm_resource_group_name
  network_interface_ids = [azurerm_network_interface.main[each.key].id]
  vm_size               = "Standard_D2s_v3"


  storage_image_reference {
    publisher = "Canonical"
    offer     = "UbuntuServer"
    sku       = "18.04-LTS"
    version   = "latest"
  }
  storage_os_disk {
    name              = "${each.key}-myosdisk1"
    caching           = "ReadWrite"
    create_option     = "FromImage"
    managed_disk_type = "Standard_LRS"
  }
  os_profile {
    computer_name  = "${each.key}-hostname"
    admin_username = "testadmin"
    admin_password = random_password.password.result
  }
  os_profile_linux_config {
    disable_password_authentication = false
  }
  tags = {
    environment = "dev01"
  }

}

resource "random_id" "server" {
  keepers = {
    azi_id = 1
  }

  byte_length = 8
}

resource "azurerm_traffic_manager_profile" "example" {
  name                   = random_id.server.hex
  resource_group_name    = var.azurerm_resource_group_name
  traffic_routing_method = "Priority"

  dns_config {
    relative_name = random_id.server.hex
    ttl           = 100
  }

  monitor_config {
    protocol                     = "http"
    port                         = 80
    path                         = "/"
    interval_in_seconds          = 30
    timeout_in_seconds           = 9
    tolerated_number_of_failures = 3
  }

  tags = {
    environment = "dev01"
  }
}

resource "azurerm_traffic_manager_endpoint" "first-vm" {
  for_each            = var.locations
  name                = "${each.key}-TF"
  resource_group_name = var.azurerm_resource_group_name
  profile_name        = "${azurerm_traffic_manager_profile.example.name}"
  target_resource_id  = "[azurerm_network_interface.main[each.key].id]"
  type                = "azureEndpoints"
  priority              = "${[each.key] == "vm1" ? 1 : 2}"
}

My error:

Error: trafficmanager.EndpointsClient#CreateOrUpdate: Failure responding to request: StatusCode=400 -- Original Error: autorest/azure: Service returned an error. 
Status=400 Code="BadRequest" Message="The 'resourceTargetId' property of endpoint 'vm1-TF' is invalid or missing. 
The property must be specified only for the following endpoint types: AzureEndpoints, NestedEndpoints. 
You must have read access to the resource to which it refers."