curl --request GET \
  --url https://api.sandbox.monite.com/v1/payable_purchase_orders/variables \
  --header 'Authorization: Bearer <token>' \
  --header 'x-monite-version: <x-monite-version>'

{
  "data": [
    {
      "object_subtype": "quote",
      "object_type": "<string>",
      "variables": [
        {
          "description": "<string>",
          "name": "<string>"
        }
      ]
    }
  ]
}