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# respond(response:)

Respond to the session after receiving and processing an APDU.

```
final func respond(response: Data) async throws
```

## Parameters

`response`

The APDU data to send as a response.

## Discussion

Your client must respond to each APDU it receives. Failing to respond throws an error. If your client disposes an APDU object without responding, the card emulation ends.

> Warning:
> Only respond to a given APDU once. Calling this method more than once raises <doc://com.apple.documentation/documentation/Swift/fatalError(_:file:line:)>. The exception to this is if the call throws ``doc://com.apple.corenfc/documentation/CoreNFC/CardSession/Error/transmissionError``. In this case, you can retry the response by calling ``doc://com.apple.corenfc/documentation/CoreNFC/CardSession/APDU/respond(response:)`` again.

---

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