<!-- source: https://secondlayer.tools/docs/api-reference#stacking-action-object -->

## The PoX-4 stacking action object

One decoded PoX-4 contract call. Which columns are set depends on `function_name`; a failed call sets only the base fields.

| Field | Type | Description |
| --- | --- | --- |
| `cursor` | string | `<block_height>:<tx_index>`. Pass as `cursor`. |
| `block_height` | integer | Stacks block the call landed in. |
| `block_time` | string · date-time · nullable | That block's timestamp. |
| `burn_block_height` | integer | Bitcoin block that Stacks block anchors to. |
| `tx_id` | string | The calling transaction. |
| `tx_index` | integer | Its position in the block. With `block_height`, the cursor. |
| `function_name` | string | PoX-4 function called, e.g. `stack-stx`. |
| `caller` | string | Transaction sender. |
| `stacker` | string · nullable | Stacker the call acts on, on delegate-side calls. Null on solo `stack-stx`, where `caller` is the stacker. |
| `delegate_to` | string · nullable | Pool operator, on `delegate-stx`. |
| `amount_ustx` | string · nullable | microSTX as a decimal string (bigint-safe): the amount locked, delegated or increased by. |
| `lock_period` | integer · nullable | Cycles locked, or extended by. |
| `pox_addr` | object | Bitcoin reward address. Every field is null when the call names none. |
| `start_cycle` | integer · nullable | First reward cycle the lock covers. |
| `end_cycle` | integer · nullable | Last reward cycle the lock covers. |
| `reward_cycle` | integer · nullable | Reward cycle named by aggregation and signer-key calls. What `/v1/index/pox/cycles` groups on. |
| `signer_key` | string · nullable | Signer public key, `0x`-prefixed hex. |
| `result_ok` | boolean | Whether the call returned `ok`. |

```json
{
  "cursor": "8647822:1",
  "block_height": 8647822,
  "block_time": "2026-07-27T18:39:09.000Z",
  "burn_block_height": 959869,
  "tx_id": "0x995fb653065c74596b63e6cc9c10fb8fa7b8f3574d5ea089b45d3e11d9e7336e",
  "tx_index": 1,
  "function_name": "stack-stx",
  "caller": "SP14S259H3AC9PXWJ8EVX9ER5NZ58R03GR4QAKHCB",
  "stacker": null,
  "delegate_to": null,
  "amount_ustx": "4491100000000",
  "lock_period": 1,
  "pox_addr": {
    "version": 6,
    "hashbytes": "0x6f0fbc92d6ad56a9d7783b7420ae6731434831e3484d82ad54afe32d7fc7ad6d",
    "btc": "bc1pdu8meykk44t2n4mc8d6zptn8x9p5sv0rfpxc9t254l3j6l7844ksz4jjcs"
  },
  "start_cycle": 139,
  "end_cycle": 139,
  "reward_cycle": null,
  "signer_key": "0x031b91a32ab90b80d40715e8875fb3dfe996aa1e6f5e62ba05d34542aa58ad43b5",
  "result_ok": true
}
```