Firebase data not displaying in tableview in xcode

I have been trying to retrieve profile data from firebase realtime database and displaying it in a table view, so far when I run the simulator the tabelview shows up blank and Failed : error 0:50 [50] shows up. I am pretty new to swift and am not sure what the problem is.

Here is my code:

import UIKit
import FirebaseDatabase
import FirebaseStorage
import FirebaseAuth

class userViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
         return profileData.count
        
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "firstName_cell",
                                                 for: indexPath)

        self.tableView.reloadData()
        cell.textLabel?.text = self.profileData[indexPath.item]
        return cell
   
    }
    
    
    
    var profileData = [String]()
    
    let storageRef = Storage.storage().reference()
    var databaseRef = Database.database().reference()
    var ref: DatabaseReference?
    @IBOutlet var tableView: UITableView!
    
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        
        ref = Database.database().reference()
        
        //let userID = Auth.auth().currentUser?.uid
        ref?.child("users").observeSingleEvent( of: .childAdded, with: { (snapshot) in
       
            let profile = snapshot.value as? String
            
            if let actualProfile = profile{
                self.profileData.append(actualProfile)
                print(self.profileData)
                self.tableView.reloadData()
            }
            
              }) { (error) in
                print(error.localizedDescription)
            }


            
        }
        
    }