const options = {method: 'GET', headers: {Authorization: 'Basic <encoded-value>'}};

fetch('https://api.opereit.ai/v1/contracts/{contract_id}/surcharges', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "data": [
    {
      "id": "<string>",
      "contract_id": "<string>",
      "slug": "fuel",
      "display_name": "Fuel surcharge",
      "billing_type": "PERCENTAGE",
      "value": "15.00",
      "currency": "EUR",
      "is_waived": true,
      "origin_country": "<string>",
      "destination_country": "<string>",
      "service_type": "<string>",
      "calculation_base": [
        "<string>"
      ]
    }
  ],
  "pagination": {
    "cursor": "<string>",
    "has_more": true
  }
}

{
  "statusCode": 401,
  "statusReasonCode": "AUTHENTICATION_REQUIRED",
  "error": "Authentication required"
}

{
  "statusCode": 404,
  "statusReasonCode": "CONTRACT_NOT_FOUND",
  "error": "Contract not found"
}