curl --fail-with-body "$THORNODE_RPC_URL" \
  --header 'content-type: application/json' \
  --data '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "simulateTransaction",
    "params": [
      "<BASE64_TRANSACTION>",
      {
        "encoding": "base64",
        "sigVerify": false,
        "replaceRecentBlockhash": true
      }
    ]
  }'

const body = {
  "jsonrpc": "2.0",
  "id": 1,
  "method": "simulateTransaction",
  "params": [
    "<BASE64_TRANSACTION>",
    {
      "encoding": "base64",
      "sigVerify": false,
      "replaceRecentBlockhash": true
    }
  ]
};

const response = await fetch(process.env.THORNODE_RPC_URL, {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify(body),
});
const { result, error } = await response.json();
console.log(result ?? error);

{
  "jsonrpc": "2.0",
  "result": {
    "context": {
      "apiVersion": "4.1.2",
      "slot": 439749205
    },
    "value": {
      "accounts": null,
      "err": null,
      "fee": 5000,
      "innerInstructions": null,
      "loadedAccountsDataSize": 149,
      "loadedAddresses": {
        "readonly": [],
        "writable": []
      },
      "logs": [
        "Program 11111111111111111111111111111111 invoke [1]",
        "Program 11111111111111111111111111111111 success"
      ],
      "postBalances": [
        777131893034520,
        1
      ],
      "postTokenBalances": [],
      "preBalances": [
        777131893039520,
        1
      ],
      "preTokenBalances": [],
      "replacementBlockhash": {
        "blockhash": "7T6Zk3mmgYodW6HNGYemPFYGAUNdyN25NgSefiRfCASH",
        "lastValidBlockHeight": 417799916
      },
      "returnData": null,
      "unitsConsumed": 150
    }
  },
  "id": 1
}