curl --request GET \
  --url https://api.example.com/aggregate-values

{
  "data": {
    "entityId": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "variableDefId": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "value": null
  }
}