Payload error in Cloud Functions for Firebase Messaging

Question

I wrote a cloud function using Cloud Functions for Firebase that sends notifications to certain topics of Firebase Messaging. The final parts of the function define the payload to be sent, then sends it:

// javascript code in cloud functions
const payload = {
      'notification': {
        'title': `${toTitleCase(name)} just logged an event`,
        'body': `${events[eventType]} for ${toTitleCase(petName)}`,
        'data': {
            'personSent': userSent 
        }
      }
    };
console.log(payload);
admin.messaging().sendToTopic(pet_Id, payload);

However, I'm getting the error log in my Firebase console:

Error: Messaging payload contains an invalid value for the "notification.data" property. Values must be strings.

When I logout the payload I confirmed it is all strings:

{ notification: 
   { title: 'Turtle Dude just logged an event',
     body: 'Walk for Beer',
     data: { personSent: 'mfsP8U0qDdQL4rrrbXp6K0YsF423' } } }

However, when I send the same payload from my iPhone app (which I'm trying to avoid since that means I have to store the messaging private key on the client side) I am able to attach the extra data I want to send just fine:

// Swift code in iPhone app
let body: [String: Any] = ["to": "/topics/\(currentPet)",
                            "priority" : "high",
                            "notification" : [
                                "body" : "\(events[eventType]) for \(petsName.localizedCapitalized)",
                                "title" : "\(myName.localizedCapitalized) just logged an event",
                                "data" : ["personSent": myId]
                              ]
                           ]

How can I accomplish adding additional data in my cloud function like I do in my Swift code?

Answer 1

As others explained in the comments, the data object should go inside payload ,
NOT inside notification .

Try the following code:

// javascript code in cloud functions
const payload = {
      'notification': {
        'title': `${toTitleCase(name)} just logged an event`,
        'body': `${events[eventType]} for ${toTitleCase(petName)}`,
      }, 
      // NOTE: The 'data' object is inside payload, not inside notification
      'data': { 
            'personSent': userSent 
      }
    };
console.log(payload);
admin.messaging().sendToTopic(pet_Id, payload);

Answer 2

Along with Diego's answer, I would like to point out a crucial detail for anyone who visits this message in the future... "Make sure to PARSE ANY ObjectId's to String when assigning it to a value for any key inside DATA" . This has pretty much been the most unfigurable problem while dealing with FCM. And was the prime factor in solving my problem.

Answer 3

Whoever might experience this error by now. Using node V14.7.0 on Windows and firebase-admin version ^9.6.0 seem to work perfectly, I had no issue. However, when deploying it on Bitnami, the error was thrown. To solve it, I had to parse the object someObject properties to be assigned to 'data' to string:

//someObject.property_throwing the error should be parsed to string

data: someObject