Cloud Functions Cant Not Get Token From Realtime Database

im trying to send message from function but its always got 'Registration token(s) provided to sendToDevice() must be a non-empty string or a non-empty array' but here is where my

Solution 1:

I think you're trying to use the value of the token property of the user who triggered the Cloud Function. In that case you don't need to attach a separate listener, as the value is already available inside the context parameter.

exports.mess = functions.database.ref('/path/{uid}')
.onWrite(event => {
    let token = event.after.child('token').val()
    const payload = {
        notification: {
            title: 'You have been invited to a trip.',
            body: 'Tap here to check it out!'
        }
    };

    return admin.messaging().sendToDevice(snapshot.val(), payload)
});