Retrieve fee

curl --request GET \
  --url https://sandbox-api.billingrails.com/v1/fees/{id} \
  --header 'Authorization: Bearer <token>'

{
  "fee": {
    "object": "fee",
    "id": "fee_IhMUl3rrZ3",
    "created_at": "2025-02-14T17:33:40.843Z",
    "type": "plan",
    "meter_id": "meter_IhMUl3rrZ3",
    "plan_id": "plan_IhMUl3rrZ3",
    "name": "Basic Plan",
    "code": "basic_plan",
    "description": "Basic plan for users",
    "invoice_name": "Basic Plan",
    "model": "standard",
    "currency": "NGN",
    "bill_timing": "advance",
    "interval": {
      "unit": "month",
      "frequency": 1
    },
    "billing_cycles": 1,
    "amount": 1000,
    "package_size": 2,
    "unit_label": "user",
    "free_units": 0,
    "active_subscriptions": 5
  }
}