curl --request PATCH \
  --url https://v1.api.flux-os.com/contracts/{id}/fees/{fee_id} \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --header 'x-user-id: <api-key>' \
  --data '
{
  "type": "<unknown>",
  "fee_category": "<unknown>",
  "currency": "<unknown>",
  "amount": null,
  "transport_leg": null,
  "measurement_unit": null
}
'

{
  "id": "<string>",
  "amount": null,
  "transport_leg": null,
  "created_at": "2023-11-07T05:31:56Z",
  "updated_at": "2023-11-07T05:31:56Z",
  "total_cost": 123
}