Need help with tKinter Scrollbar, doesnt attach to listbox

from tkinter import *

app = Tk()

label1_text = StringVar()
part_label = Label(app, bg='#dfe3ee', text='Check1', font=('bold',12), pady=10, padx=20)
part_label.grid(row=0, column=0, sticky=W)
label1_entry = Entry(app, textvariable=label1_text)
label1_entry.grid(row=0, column=1)

label2_text = StringVar()
part_label = Label(app, bg='#dfe3ee', text='Check1', font=('bold', 12), pady=7, padx=20)
part_label.grid(row=1, column=0, sticky=W)
label2_entry = Entry(app, textvariable=label2_text)
label2_entry.grid(row=1, column=1)

label3_text = StringVar()
part_label = Label(app, bg='#dfe3ee', text='Check3', font=('bold', 12), pady=20)
part_label.grid(row=0, column=2)
label3_entry = Entry(app, textvariable=label3_text)
label3_entry.grid(row=0, column=3)

label4 = StringVar()
part_label = Label(app, bg='#dfe3ee', text='check4', font=('bold', 12), pady=7)
part_label.grid(row=1, column=2)
label4_entry = Entry(app, textvariable=label4)
label4_entry.grid(row=1, column=3)

B1_btn = Button(app, bg='#cd8de5', text='Button1',font=('bold', 11), width=12)
B1_btn.grid(row=3, column=1, padx=0, pady=5)

B2_btn = Button(app, bg='#cd8de5', text='Button2',font=('bold', 11), width=12 )
B2_btn.grid(row=4, column=1, padx=0, pady=5)

B3_btn = Button(app, bg='#d5a6e6', text='close',font=('bold', 11), width=12)
B3_btn.grid(row=50, column=2, sticky='E')

output_list = Listbox(app, height=20, width=100, border=5)
output_list.grid(row=20, column=0, columnspan=3, rowspan=6, pady=20, padx=20)

scrollbar = Scrollbar(app)
scrollbar.grid(row=20, column =3, rowspan=5, sticky=(N+S))

output_list.configure(yscrollcommand=scrollbar.set)
scrollbar.configure(command=output_list.yview)

app.title('Test Tool')
app.geometry('900x900')
app.configure(bg='#dfe3ee')

app.mainloop()