when I use this function which triggered when something changes in /drivers/{wilayaid}/{driverid}/proposed .. it gives me TypeError: change.after.get is not a function

exports.sendNotification = functions.database.ref('/drivers/{wilayaid}/{driverid}/proposed').onUpdate(async (change) => {

    const fcm = change.after.get('fcm');

    var message = {
        notification: {
            title: "CLIQUE ICI",
            body: "NOUVELLE OFFRE DE TRANSPORTATION",
        },
        token: fcm,
    }

    let response = await admin.messaging().send(message);
    console.log(response);
    console.log(fcmToken);
    
});

I dont know why !!!