terraform plan error : Argument not expected here - google-cloud-platform

Question

I am trying to create custom IAM roles for different environments, with different set of permissions for dev and prod, in Google Cloud Platform. My folder structure is as follows:
iamroles (root folder)
-- main.tf
-- variables.tf
--customiamroles(folder)
----main.tf
--environments
----nonprod
------main.tf
------variables.tf
----prod
------main.tf
------variables.tf
The main.tf in the root folder has the below code:
iamroles/main.tf
/*
This is the 'main' Terraform file. It calls the child modules to create roles in the corresponding environments
*/
provider "google" {
credentials = file("${var.project_id}.json")
project = var.project_id
region = var.location
}
module "nonprod" {
source = "./environments/nonprod"
}
iamroles/variables.tf
variable "project_id"{
type = string
}
variable "location" {
type = string
default = "europe-west3"
}
iamroles/environments/nonprod/main.tf
module "nonprod" {
role_details = [{
role_id = "VS_DEV_NONPROD_CLOUDSQL",
title = "VS DEVELOPER NON PROD CLOUD SQL",
description = "Role which provides limited view and update access to Cloud SQL",
permissions = var.developer_nonprod_sql
},
{
role_id = "VS_DEV_NONPROD_APPENGINE",
title = "VS DEVELOPER NON PROD APPENGINE",
description = "Appengine access for developers for non production environments to View, Create and Delete versions, View and Delete instances, View and Run cron jobs",
permissions = var.developer_nonprod_appengine
}]
source = "../../customiamroles"
}
iamroles/environments/nonprod/variables.tf
variable "role_details" {
type = list(object({
role_id = string
title = string
description = string
permissions = list(string)
}))
}
variable "developer_nonprod_sql" {
default = ["cloudsql.databases.create","cloudsql.databases.get"]
}
variable "developer_nonprod_appengine" {
default = ["appengine.applications.get","appengine.instances.get","appengine.instances.list","appengine.operations.*","appengine.services.get","appengine.services.list"]
}
iamroles/customiamroles/main.tf
# Creating custom roles
resource "google_project_iam_custom_role" "vs-custom-roles" {
for_each = var.role_details
role_id = each.value.role_id
title = each.value.title
description = each.value.description
permissions = each.value.permissions
}
While executing terraform plan from iamroles folder, i am getting the below exception:
I am new to terraform, learning for the past two days. I could use some help to understand what I am doing wrong.