Terraform for_each with YAML var file for queues

Trying to spin up multiple queues using for_each mapped to a YAML variable file. The plan crashes with `Inappropriate value for attribute “queues”: element 0: string required.

module "queues" {
 for_each = var.queue_defs
 ... 
}

Var is loaded via yamldecode. Need the HCL syntax to flatten this properly.