iOS Firebase - How to obtain and save the URL of a photo?

I want to save in Firebase the url of a photo that is selected by the user. Xcode is showing me the following error: Use of unresolved identifier 'profileImageUrl'; I do not know how to solve it.

@IBAction func signUpBtn(_ sender: Any) {
    Auth.auth().createUser(withEmail: emailTextField.text!, password: passwordTextField.text!, completion: { (user, error) in
        if error != nil {
            print("error")
            return
        }


        let userID = Auth.auth().currentUser!.uid

        let storageRef = Storage.storage().reference(forURL: "gs://ejemploProyecto.appspot.com").child("profile_image").child(userID)
        if let profileImg = self.selectedImage, let imageData = self.selectedImage?.jpegData(compressionQuality: 0.1){
            storageRef.putData(imageData, metadata: nil, completion: { (metadata, error) in
                if error != nil {
                    return
                }


                storageRef.downloadURL { (url, error) in
                    guard let profileImageUrl = url else {
                        // Uh-oh, an error occurred!
                        return
                    }
                }

                let ref = Database.database().reference()
                let usersReference = ref.child("users")
                let newUserReference = usersReference.child(userID)
                newUserReference.setValue(["username": self.usernameTextField.text!, "email": self.emailTextField.text!, "profileImageUrl": profileImageUrl])

            })
        }
    })
}