Updating child in firebase not working as expected - swift

Question

I am trying to save data into firebase, by first generating a child using .childByAutoId() and then update the child with the necessary data. But it doesn't seem to work as expected.
The structure I am trying to achieve is
events
attendees
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userEmail: "user#user.com"
userName: "User name"
userPhone: "0864567182"
Here's what I have done so far:
guard let fee = events?["eventFee"] else {
return
}
guard let key = events?["eventKey"] else {
return
}
guard let eventTitle = events?["title"] else {
return
}
if fee == "0" {
var values = [String: String]()
self.ref = Database.database().reference()
let attendeekey = ref.child("events").child(key).child("attendees").childByAutoId().key
let userDetails = UserDetails()
for user in userDetails.currentUserDetails {
guard let userEmail = user.email else {
return
}
guard let firstName = user.firstName, let lastName = user.lastName else {
return
}
guard let userPhone = user.phoneNo else {
return
}
let userName = "\(firstName) \(lastName)"
values = ["userEmail": userEmail, "userName": userName, "userPhone": userPhone as! String]
}
ref.updateChildValues(["events/\(key)/attendees/\(attendeekey)": values], withCompletionBlock: {
(err, ref) in
if err != nil {
self.displayAlertMessage(message: err as! String, title: "Oops!")
//print(err ?? "An error occured")
return
}
let message = "You have successfully registered for \(eventTitle)"
self.displayAlertMessage(message: message, title: "Success!")
})
}
Is anything wrong with my approach?