# rollup.emitException

Signals that the current request **could not be processed** — a structural failure, not a business-rule rejection. The exception payload is surfaced to the outside world; the machine treats the request as failed.

Prefer the gentler paths first: return `false` from a [`run`](/cmio/reference/run) handler to reject an input, or throw (which `run` converts to a report plus rejection). `emitException` is the last resort for "this application cannot meaningfully continue with this request".

## Usage

```ts twoslash
import { Rollup } from '@deroll/cmio';
const rollup = new Rollup();
// ---cut---
rollup.emitException(Buffer.from('unrecoverable: state corrupted'));
```

## Returns

`void`

## Parameters

### payload

* Type: `BytesLike` — 0x-prefixed hex string, `Buffer` or `Uint8Array`
* Required

Diagnostic data describing the failure.

## Errors

| Condition | Error |
| --- | --- |
| Malformed hex string / wrong argument type | `TypeError` |
| Underlying libcmt failure | `RollupError` with negative `errno` |