# Troubleshooting

This guide shows you how to troubleshoot common Twilio Communications API issues. It explains where error information appears, how to interpret it, and what to do next.

## Where to find errors

Errors can appear in three main places:

* API responses
* Twilio Console
* Event logs

## API responses

If a request fails, the API returns a `4xx` or `5xx` error in the response body.

* `400` errors indicate that your request is invalid. The response includes a message that explains the problem.
* `500` errors indicate an internal Twilio error.

If you need help with a `400` or `500` error, contact [comms-api@twilio.com](mailto:comms-api@twilio.com).

For a complete list of error codes and descriptions, see the [API errors documentation](/docs/api/errors).

## Twilio Console

Use the [Console Debugger](https://console.twilio.com/us1/monitor/logs/debugger/errors) to find errors related to message delivery, opt-outs, and other post-request issues.

## Event logs

[Twilio Event Streams](/docs/events) deliver real-time events to webhooks and other destinations, such as AWS Kinesis and Segment. You can subscribe to the event types you need. If an event fails to deliver, Twilio queues the event and retries when the destination becomes available.

### Twilio Communications API event types

You can subscribe to these Communications API-specific event types:

**Operations**

* `com.twilio.comms-api.operation.processing`
* `com.twilio.comms-api.operation.completed`

**Messages**

* `com.twilio.comms-api.message.queued`
* `com.twilio.comms-api.message.sent`
* `com.twilio.comms-api.message.failed`
* `com.twilio.comms-api.message.delivered`
* `com.twilio.comms-api.message.undelivered`
* `com.twilio.comms-api.message.read`

You can also use events from downstream services, such as Programmable Messaging. These events include SM/MM SIDs for individual message deliveries.

See the [outbound Messaging delivery status events](/docs/events/event-types/messaging/outbound-message) for more details:

* `com.twilio.messaging.message.delivered`
* `com.twilio.messaging.message.failed`
* `com.twilio.messaging.message.queued`
* `com.twilio.messaging.message.read`
* `com.twilio.messaging.message.sent`
* `com.twilio.messaging.message.undelivered`

For error logging, subscribe to the [error-logs event type](/docs/events/event-types/errors/error-logs):

* `com.twilio.error-logs.error.logged`