curl --request POST \
  --url https://api.production.hyperoru.com/api/factors/custom \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "context": {},
  "expression": "<string>",
  "symbol": "<string>"
}
'

{
  "id": 123,
  "name": "<string>",
  "category": "<string>",
  "description": "<string>",
  "source": "<string>"
}