问颤振通知/解析错误:意外令牌管理

EN

const functions = require('firebase-functions');
const admin = require('firebase-admin');

admin.initalizeApp(functions.config().firebase);

var msgData;

//listen for new uploades
exports.recipeTrigger = functions.firestore.document('item/{itemId}').onCreate(async(snapshot) => {
msgData = snapshot.data();

//get dat from the user that uploaded the item
await admin.firestore().collection('User/' + msgData.uid).get().then((snapshots) => {
    var users = [];
    var tokens = [];
    if (snapshot.empty) {
        console.log('No Users');
        return null;
    } else {
        //get every user uid
        users = snapshots.data().subscribers;
        for (user of users) {
            //user should be the uid
            admin.firestore().collection('User/' + user).get().then((snap) => {
                for (var token of snap.docs) {
                    //add devicetoken to a list Avoid nesting promises
                    tokens.add(token.data().token);
                }
                return tokens;
            }).catch(error => { print(error) })
            return users;
        }
        //specify message content
        var payload = {
                "notification": {
                    "title": "From" + snapshots.data().displayName,
                    "body": "I uploaded a new Recipe",
                    "sound": "default",
                },
                "data": {
                    "senderName": snapshots.data().displayName,
                    "message": snapshots.data().displayName + "uploaded a new Recipe",
                }
            }
            //send message to devicetokens
        return admin.messaging().sendToDevice(tokens, payload).then((response) => {
            console.log('Notifications send');
            return response;
        }).catch((er) => {
            console.log(er);
        });
    }
}).catch(error => { print(error) });
})