firebase_messaging: 4.0.0+1

There is a different notification format for iOS and Android - parameter for onMessage callback.

iOS:
{google.c.a.c_l: 20190226 - en, google.c.a.c_id: 2741820249588377404, gcm.n.e: 1, google.c.a.e: 1, count: 2, gcm.message_id: 0:1552019268226658%929750ef929750ef, path: lists_custom/2019-02-26/list, action: list, google.c.a.udt: 0, google.c.a.ts: 1552019268, aps: {alert: 2 new flowers were added to the herbary}, click_action: FLUTTER_NOTIFICATION_CLICK}

Android:
{notification: {title: null, body: 2 new flowers were added to the herbary}, data: {action: list, path: lists_custom/2019-02-26/list, count: 2, click_action: FLUTTER_NOTIFICATION_CLICK}}