curl --request POST \
  --url https://v1.api.flux-os.com/measurements/units/convert \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --header 'x-user-id: <api-key>' \
  --data '
{
  "value": 123,
  "from_unit_id": 123,
  "to_unit_id": 123,
  "product_category_id": 123
}
'

{
  "data": {
    "product_category": {
      "id": 123,
      "name": "<string>"
    },
    "from": {
      "value": 123,
      "measurement_unit": {
        "id": 123,
        "name": "<string>",
        "abbreviation": "<string>"
      }
    },
    "to": {
      "value": 123,
      "measurement_unit": {
        "id": 123,
        "name": "<string>",
        "abbreviation": "<string>"
      }
    },
    "formula": "<string>"
  }
}