---
title: 2018: iMessage app messages can only be sent over iMessage | API Docs
description: An imessage_app part was sent while SMS or RCS was explicitly requested.
---

iMessage app messages can only be sent over iMessage. The request included an `imessage_app` part while explicitly requesting SMS or RCS. This is an HTTP 409 error.

## Troubleshooting

- Omit `preferred_service` — it defaults to iMessage for app parts — or set it to `iMessage`
- iMessage app parts never fall back to SMS/RCS. If the recipient isn’t reachable over iMessage, the send instead fails asynchronously with a `message.failed` webhook carrying code [4005](/error/codes/4xxx/4005/index.md)
- [Check iMessage capability](/guides/messaging/protocol-selection#protocol-capabilities/index.md) before sending

## Related

- [iMessage Apps](/guides/messaging/imessage-apps/index.md)
- [Protocol Selection](/guides/messaging/protocol-selection/index.md)
- [Error Codes](/error/index.md)