Terraform Modules - Unable to Access variable from root

I am trying to pass a variable from the root module to a child module with the following syntax and i'm unable to do that:

└── Terraform
            ├── main.tf
            ├── variable.tf
    └── module
                ├──main.tf
                ├── variable.tf

Terraform Version:

Terraform v0.11.11
+ provider.openstack v1.15.0

Terraform Configuration Files /Terraform/main.tf:

provider "openstack" {
openstack_user_name         = "${var.openstack_user_name}"
openstack_tenant_name   = "${var.openstack_tenant_name}"
openstack_password      = "${var.openstack_password}"
openstack_auth_url          = "${var.openstack_auth_url}"
domain_name             = "${var.domain_name}"
}
module "testMod" {
name                    = "${var.name}"
imageId                     = "${var.imageId}"
flavor_name                 = "${var.flavor_name}"
openstack_keypair   = "${var.openstack_keypair}"
tenant_network_id           = "${var.tenant_network_id}"
tenant_network      = "${var.tenant_network}"
source = "./modules"
}

/Terraform/variable.tf:

variable "name" {default = "XXX"}
variable "imageId" {default = "11-22-33"}
variable "flavor_name"{default = "flavor"}
...

/Terraform/modules/main.tf:

resource "openstack_compute_instance_v2" "test" {
 name               = "${var.name}"
imageId                 = "${var.imageId}"
flavor_name             = "${var.flavor_name}"
openstack_keypair       = "${var.openstack_keypair}"
security_groups     =   ["default"]

network {
tenant_network_id       = "${var.tenant_network_id}"
tenant_network      = "${var.tenant_network}"
    }
}

/Terraform/modules/variable.tf:

variable "name" {}
variable "imageId" {}
variable "flavor_name" {}
variable "openstack_keypair" {}
variable "tenant_network_id"{}
variable "tenant_network" {}

Actual Behavior

Error: module.testMod.openstack_compute_instance_v2.test: : invalid or unknown key: imageId

Steps to Reproduce

1. terraform init
2. terraform apply

Unsure what is going wrong here

The error is alerting you to the unknown keyimageId. This message is accurate as, in fact, the key should be image_id. You can check the Terraform openstack_compute_instance_v2 resource documentation and note the presence of the image_id argument.

Your code would then look like:

resource "openstack_compute_instance_v2" "test" {
  name              = "${var.name}"
  image_id          = "${var.imageId}"
  flavor_name       = "${var.flavor_name}"
  openstack_keypair = "${var.openstack_keypair}"
  security_groups   = ["default"]
}