i created this structure like this below.

`func sendMessage(_ message: Message) {
    let document = db.collection("messages")
        .document(message.senderId)
        .collection(message.receiverId)
        .document()
    
    let messageData = ["fromId": message.senderId, 
   "toId": message.receiverId, "content":  message.content, 
   "timestamp": message.timestamp] as [String : Any]
    
    document.setData(messageData) { error in
        if let error = error {
            print("ERROR SAVING MESSAGE INTO FIRESTORE (error.localizedDescription)")
            return
        }
    }
    
    let recipientMessageDocument = db.collection("messages")
        .document(message.receiverId)
        .collection(message.senderId)
        .document()
    
    recipientMessageDocument.setData(messageData) { error in
        if let error = error {
            print("ERROR SAVING MESSAGE INTO FIRESTORE (error.localizedDescription)")
            return
        }
    }`

and successfully fetch the messages like this:

`func fetchMessages(_ fromId: String, _ toId: String) {
    db.collection("messages")
        .document(fromId)
        .collection(toId)
        .addSnapshotListener { querySnapshot, error in
            if let error = error {
                print("FAILED TO LISTEM FOR MESSAGES: (error.localizedDescription)")
                return
            }
            
            querySnapshot?.documentChanges.forEach({ change in
                if change.type == .added {
                    let data = change.document.data()
                    DispatchQueue.main.async {
               let newMessage = ChatMessage(documentId: change.document.documentID, data: data)
                    self.messages.append(newMessage)
                    }
                }
            })
        }`

but when i want to pull all the receiverId i circled below in the picture, i get “document does not exist” error. How can i get those receiverId s?

This is how i try to fetch the receiverIds. Actually this function is for getting userNames but at the beginning of the function i can’t get content of the subcollection.