Can't connect my project Cannot convert value of type 'User' to expected argument type '[String : Any]'

Question

I'm trying to connect with Firebase and I have an error.

This is my UserViewModel:

import Foundation
import FirebaseAuth
import FirebaseFirestore

class UserViewModel: ObservableObject {
    // MARK: State
    @Published var user: User?
    
    // MARK: Properties
    private let auth = Auth.auth()
    private let db = Firestore.firestore()
    var uuid: String? {
        auth.currentUser?.uid
    }
    var userIsAuthenticated: Bool {
        auth.currentUser != nil
    }
    var userIsAuthenticatedAndSynced: Bool {
        user != nil && self.userIsAuthenticated
    }
    
    // MARK: Firebase Auth Functions
    func signIn(email: String, password: String) {
        auth.signIn(withEmail: email, password: password) { [weak self] result, error in
            guard result != nil, error == nil else { return }
            // Successfully authenticated the user, now attempting to sync with Firestore
            DispatchQueue.main.async {
                self?.sync()
            }
            
        }
    }
    
    func signUp(email: String, username: String, password: String) {
        auth.createUser(withEmail: email, password: password) { [weak self] result, error in
            guard result != nil, error == nil else { return }
            DispatchQueue.main.async {
                self?.add(User(username: username))
                self?.sync()
            }
        }
    }
    
    func signOut() {
        do {
            try auth.signOut()
            self.user = nil
        } catch {
            print("Error signing out the user: \(error)")
        }
    }
    
    // Firestore functions for User Data
    private func sync() {
        guard userIsAuthenticated else {
            return
        }
        db.collection("users").document(self.uuid!).getDocument { (document, error) in
            guard document != nil, error == nil else {
                return
            }
            do {
                try self.user = document!.data(as: User.self)
            } catch {
                print("Sync error: \(error)")
            }
            
        }
        
    }
    
    private func add(_ user: User) {
        guard userIsAuthenticated else {
            return
        }
        do {
            let _ = try db.collection("users").document(self.uuid!).setData(user)
        } catch {
            print("Error adding: \(error)")
        }
    }
    
    private func update() {
        guard userIsAuthenticatedAndSynced else {
            return
        }
        do {
            let _ = try db.collection("users").document(self.uuid!).setData(self.user)
        } catch {
            print("Error updating: \(error)")
        }
        
        
    }
}

and my User model:

import Foundation


struct User: Codable {
    var username: String
}

My errors are: Cannot convert value of type 'User' to expected argument type '[String : Any]'

What do I do to fix these problems? How to change my code properly? It occurs in the add, sync and update functions.