const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({reason: '<string>'})
};

fetch('https://api.keystoneos.xyz/v1/settlements/{settlement_id}/reject', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "idempotency_key": "<string>",
  "platform_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "environment_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "template_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "template_version": 123,
  "external_reference": "<string>",
  "settlement_type": "<string>",
  "parties": [
    {
      "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "role": "<string>",
      "platform_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "environment_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "external_reference": "<string>",
      "name": "<string>",
      "wallet_address": "<string>",
      "chain_id": 123,
      "asset_provider": "<string>",
      "status": "<string>",
      "confirmed_at": "2023-11-07T05:31:56Z",
      "wallet_address_hint": "<string>",
      "counterparty_reference": "<string>",
      "created_at": "2023-11-07T05:31:56Z",
      "updated_at": "2023-11-07T05:31:56Z"
    }
  ],
  "legs": [
    {
      "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "settlement_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "leg_type": "<string>",
      "instrument_id": "<string>",
      "chain_id": 123,
      "token_standard": "<string>",
      "quantity": "<string>",
      "direction": "<string>",
      "party_role": "<string>",
      "status": "<string>",
      "external_reference": "<string>",
      "created_at": "2023-11-07T05:31:56Z",
      "updated_at": "2023-11-07T05:31:56Z"
    }
  ],
  "state": "<string>",
  "timeout_at": "2023-11-07T05:31:56Z",
  "created_at": "2023-11-07T05:31:56Z",
  "updated_at": "2023-11-07T05:31:56Z"
}