Amazon web services – Terraform backend block issue

I am trying to setup terraform backend.tf for each environment while running init command but terraform init is not able recognize backend block inside backend.tf file. Here is my folder structure

project --|
          |- env/--|-dev/------|-backend.tf
                               |-terraform.tfvar
                   |- stage/---|-backend.tf
                               |-terraform.tfvar
                   |-main.tf
                   |-output.tf
                   |-variables.tf
          |-modules/-|-lambda--|----python/
                               |----zip/
                               |--main.tf
                               |--output.tf
                               |--variables.tf
                               |--requirement.tf

I have kept backend.tf for each environment and running my terraform command from env/ folder.

here is init command project/dev> terraform init -reconfigure -backend-config="dev/backend.tf" however terraform is not able to recognize backend.tf from dev folder.

This is my backend.tf file

terraform {
  backend "s3" {
    bucket         = "bucket-terraform"
    key            = "service-513/terraform.tfstate"
    region         = "us-west-2"
    dynamodb_table = "table-terraform"
  }
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

After running Terraform init, here is the warning:

╷
│ Warning: Missing backend configuration
│ 
│ -backend-config was used without a "backend" block in the configuration.
│ 
│ If you intended to override the default local backend configuration,
│ no action is required, but you may add an explicit backend block to your
│ configuration to clear this warning:
│ 
│ terraform {
│   backend "local" {}
│ }
│ 
│ However, if you intended to override a defined backend, please verify that
│ the backend configuration is present and valid.
│ 
╵

No idea, why it is happening. I would appreciate if anyone can guide me in right direction.