curl --request GET \
  --url https://realtime-api.voiceflow.com/v1/stable/function-variable/{variableID} \
  --header 'Authorization: Bearer <token>'

{
  "variable": {
    "id": "<string>",
    "name": "<string>",
    "createdAt": "2023-11-07T05:31:56Z",
    "updatedAt": "2023-11-07T05:31:56Z",
    "functionID": "<string>",
    "description": "<string>"
  }
}