> For the complete documentation index, see [llms.txt](https://docs.payments.thalescloud.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.payments.thalescloud.io/transit-digitization/implement-google-transit/account-based-ticketing-abt/message-notification.md).

# Message Notification

Notifications are triggered by Transit Issuer willing to send messages to specific users / digital cards.

This section provides an overview of the workflow, including detailed steps, sequence diagrams, and potential error scenarios.

### Workflow <a href="#workflow" id="workflow"></a>

Below are the high level steps of the message notification workflow:

1. **Notification initiation** : The Transit Issuer instructs D1 Transit to send a message to a targeted digital card.
2. **Wallet notification**: D1 Transit uses Google notification API in order to send a push notification to the right wallet.
3. **Message retrieval**: Device connects to Google server which connects to D1 Transit platform in order to retrieve the content of the message.

### Sequence Diagram <a href="#sequence-diagram" id="sequence-diagram"></a>

#### Notification initiation <a href="#notification-initiation" id="notification-initiation"></a>

The Transit issuer instructs D1 Transit to send a message to the specified digital card using handleEvent API.

#### Device notification and Message retrieval <a href="#device-notification-and-message-retrieval" id="device-notification-and-message-retrieval"></a>

D1 Transit platform uses Google messagesUpdated API to send a push notification to the wallet. The device, through Google server, connects to D1 Transit in order to retrieve the message content details which D1 Transit pulls from Transit Issuer.

**Error Scenarios**

**Device is offline**

If the device is offline, the request to notify the message is queued and will be sent to the device as soon as it reconnects.

<figure><img src="/files/x0AitUBoUvYr5FkVn7qo" alt=""><figcaption></figcaption></figure>


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