It looks like you need to do some additional setup.
Conversion events
When composing a notification, it is important to think ahead and define which metric to use to assess its effectiveness. A Conversion event is an event or user action that you want to track to further measure and evaluate.
A built-in Notifications funnel analysis automatically reports Notification sent and Notification opened events. You can provide an optional conversion event that you want to analyze with the Notifications funnel analysis.
An Analytics User Property firebase_last_notification is automatically created when you send a notification from the Notifications console the first time. This identifies the most recent notification opened by the user, allowing proper notification attribution of the conversion events.
See Conversion Events to learn more conversion events and steps to take to enable conversion.
Prerequisite: Make sure your app has integrated the Firebase Cloud Messaging SDK, which enables automatic reporting of these notification-related events for the funnel analysis.
Following the link to learn more about 'Conversion Events' you'll read:
Enable events as conversions
Conversions are your most important events. By designating an event as a conversion, you facilitate attribution reporting and postback capacity on that event. Additionally, conversion events are uploaded immediately by the SDK in order to make them actionable more quickly. You may add up to 10 events as conversions.
To designate an event as a conversion:
In Firebase, navigate to your app. In Analytics, click Events, then click Network Settings. In the row for the event, click the selector menu action menu (far right of the row), then click Enable conversion.
Once an event has been enabled as a conversion, it is available in ATTRIBUTION → CONVERSION EVENTS. Attribution reporting begins for that event at the time you enable it as a conversion.
To see AdWords-attributed Conversion Events in your attribution reports, import the Firebase Conversion Event to AdWords. Once you have linked your project to AdWords, then those conversion events will also be available in AdWords. You can import them under Tools → Conversions → Firebase.
Note: The VALUE event parameter supplied with conversion events must be a number, and it must be accompanied by a currency code.
