Collect DTMF input with optional playback

**Rate limit: Per command** · **Burst:** 4 · **Refill:** 0.8 req/s Collect a complete DTMF response from the caller and optionally play audio prompts first. The operation groups the caller's keys and applies the configured digit-count, timeout, terminator, and regular-expression validation rules. The platform validates and prepares every prompt URL before admitting the command. An unavailable prompt returns a synchronous HTTP error and does not trigger a webhook. A `202 Accepted` response means that the command was queued. The application stores its `operation_uuid` and matches it to the same field in the terminal `digits.collected` event. The platform runs exactly one prompt-and-collect cycle and emits one `digits.collected` event with the collected value and outcome `status`. It does not retry the cycle. The application inspects `status` and submits another command when needed, such as a command with an invalid-PIN prompt after `status: invalid`. The platform also emits a `dtmf.received` event immediately for every key press, whether or not a collection is active. Each event contains one key and its `duration_ms`; it does not group digits or apply collection rules. These events continue during a collection. **Triggered webhook:** `digits.collected`. This POST and its cancel DELETE each use a separate rate-limit bucket with the same configuration. See [Keypad input lifecycle events](/api/keypad-input#lifecycle-events) for complete payload schemas and examples.