curl --request POST \
  --url https://api.rivermarkets.com/v1/custom-assets \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "subaccount_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "name": "<string>",
  "description": "<string>",
  "river_ids": [
    123
  ]
}
'

{
  "custom_asset_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "subaccount_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "name": "<string>",
  "members": [
    {
      "river_id": 123,
      "exchange_value": 123,
      "exchange_name": "<string>",
      "tick_size_price": 123,
      "tick_size_qty": 123,
      "minimum_order_size": 123,
      "neg_risk": true,
      "name": "<string>",
      "status": "active",
      "ticker": "<string>",
      "token_id_yes": "<string>",
      "token_id_no": "<string>",
      "slug": "<string>",
      "expiration_datetime": "2023-11-07T05:31:56Z",
      "neg_risk_id": "<string>",
      "condition_id": "<string>",
      "description": "<string>",
      "category": "Other",
      "rank": 123
    }
  ],
  "inserted_at": "2023-11-07T05:31:56Z",
  "updated_at": "2023-11-07T05:31:56Z",
  "description": "<string>"
}