main.tf

terraform {
  required_providers {
    google = {
      source = "hashicorp/google"
      version = "3.51.0"
    }
  }
}

provider "google" {
  // Only needed if you use a service account key
  credentials = file(var.credentials_file_path)

  project = var.project_id
  region  = var.region
  zone    = var.main_zone
}

module "google_networks" {
  source = "./networks"

  project_id = var.project_id
  region     = var.region
}

...