Terraform module implementation issue- no definition was found

Hello,

I'm running into the following issue when trying to use modules..

The error is for both tag names - costalloc_tags and default_tags (which worked fine before modules)

"The argument "costalloc_tags" is required, but no definition was found.

Running Terraform.exe apply -var-file="./dev/terraform.tfvars"

./dev/terraform.tfvars

default_tags ={
    "Environment" = "WELP-DEV-CORP",
"managed by" = "terraform"
}
costalloc_tags ={
    "CostAlloc" = "WELP-DEV-CORP-INFRA"
}

main.TF (Root)

module "VPC" {
source = "./modules/network"
cidr_block= var.vpc_cidr
enable_dns_hostnames= true
tags = merge(
var.default_tags,
var.costalloc_tags
)
}

variables.tf (Root)

variable "default_tags"{
type = map
}
variable "costalloc_tags"{
type = map    
}

.\modules\network\main.tf

resource "aws_vpc" "VPC" {
cidr_block= var.vpc_cidr
enable_dns_hostnames= true
tags = merge(
var.default_tags,
var.costalloc_tags
)
}
 

.\modules\network\variables.tf

variable "default_tags"{
type = map
}
variable "costalloc_tags"{
type = map    
}