Given this module input:

variable "port_mapping_metadata" {
  type = map(object({
    target_type                       = optional(string, "instance")
    ssl_policy                        = optional(string)
    listener_cert_arn                 = optional(string)
    additional_SNI_listener_cert_arns = optional(list(string),[])
    ...

I’m trying to create a resource per port_mapping_metadata (if not null, keys may be duplicates across resources), per item in additional_SNI_listener_cert_arns (if not empty). I have tried writing the resource as with a for_each as follows:

resource "aws_lb_listener_certificate" "additional_SNI_listener_certs" {
  for_each = {
    for k, v in var.port_mapping_metadata : k => {
      for index, cert_arn in try(v.additional_SNI_listener_cert_arns, []) : "${k}-${index}" => cert_arn
    }
    if try(v.additional_SNI_listener_cert_arns, []) != [] && try(v.additional_SNI_listener_cert_arns, null) != null
  }
  ##this _should_ be "{ "listener_name-0" = "arn1" , ... }"

  listener_arn   = aws_lb_listener.all[element(split("-", each.key), 0)].arn ##this should be "listener_name"
  certificate_arn = each.value ##this should be "arn1"
}

But for some reason I get the error:

│ Error: Invalid index
│ 
│   on .terraform/modules/load_balancer/load_balancer.tf line 235, in resource "aws_lb_listener_certificate" "additional_SNI_listener_certs":
│  235:   certificate_arn = each.value["cert_arn"]
│     ├────────────────
│     │ each.value is object with 2 attributes
│ 
│ The given key does not identify an element in this collection value.

I can’t understand why each.value in the resource is not a single string arn1.