tk registration, type error when clicking button

Question

I've written a code for login / registration.

When ran a "sign-in page" pops up it has 2 entries(User name & Password) and 2 buttons (login, sign up). when you click login it prints the results to IDLE(even if nothing has been typed). Clicking sign up opens a page called the Registration page. It includes 3 entries (username, password, email address) ???? 2 buttons (continue and " "). I think that is supposed to be a cancel option I never finished working on.

issue appears to come from (lines30-32)

    tk.Button(reg, text="Continue", command=onSignup).grid(row=4, column=2)
    reg_cont = tk.Button(reg)
    reg_cont.grid(row=4,column=3)

Full Code

import tkinter as tk


def validate_login(username, password):
    print("username entered :", username.get())
    print("password entered :", password.get())

def onSignup(UserName,EncryptedPassword):
  f = open(UserName,"w")
  f.write(EncryptedPassword)
  f.close()

def open_win():
    reg = tk.Toplevel(root)
    reg.title("Registration Page")
    reg.geometry(f'600x400+{int(reg.winfo_screenwidth()/2-600/2)}+{int(reg.winfo_screenheight()/2-400/2)}')

    tk.Label(reg, text="User Name").grid(row=0, column=1)
    reg_un = tk.Entry(reg)
    reg_un.grid(row=0, column=2)

    tk.Label(reg, text="Password").grid(row=1, column=1)
    reg_pw = tk.Entry(reg)
    reg_pw.grid(row=1, column=2)

    tk.Label(reg, text="Email Address").grid(row=2, column=1)
    reg_email = tk.Entry(reg)
    reg_email.grid(row=2, column=2)

    tk.Button(reg, text="Continue", command=onSignup).grid(row=4, column=2)
    reg_cont = tk.Button(reg)
    reg_cont.grid(row=4,column=3)


root = tk.Tk()
root.title('Sign in Page')
root.geometry(f'600x400+{int(root.winfo_screenwidth()/2-600/2)}+{int(root.winfo_screenheight()/2-400/2)}')

tk.Label(root, text="User Name").grid(row=0, column=1)
un = tk.Entry(root)
un.grid(row=0, column=2)

tk.Label(root, text="Password").grid(row=1, column=1)
pw = tk.Entry(root, show='*')
pw.grid(row=1, column=2)

tk.Button(root, text="Login", command=lambda u=un, p=pw: validate_login(u, p)).grid(row=4, column=1)
tk.Button(root, text="Sign up", command=open_win).grid(row=4, column=2)

The issue I'm having aside from the button I dont remember adding... is when I click "continue" on the Registration page I get an error: TypeError: onSignup() missing 2 required positional arguments: 'UserName' and 'EncryptedPassword'

Nothing happens when I click the blank button (next to continue on the registration page)

this seems to point at lines(8-11)

def onSignup(UserName,EncryptedPassword):
  f = open(UserName,"w")
  f.write(EncryptedPassword)
  f.close()

I believe this is supposed to be opening a new file and writing the username/password(encrypted). and when you attempt to sign in it checks the information saved. currently don't have anything set to happen when you login.