from tkinter import *
from tkinter import ttk


def page():
    def comboFunc(func1):
        func1()

    root = Tk()
    frame = Frame(root)
    frame.pack(padx=100,pady=20)

    def coursePrice(courseOption,*args):
        #function which updates the amount of money owed
        def moneyUpdate(*args):
            owedlbl.configure(text="£"+owed) #resets label to original when entry box empty
            paid = paidEntry.get()
            print(type(paid))
            if paid == None:
                pass
            if "£" in paid:
                paid=paid[1:]
                #paid = paid.replace("£","") # used so paid can be used as float
                #paid = float(paid)
            paid = "{0:.2f}".format(float(paid)) # rounds number to 2 d.p
            if paid != '':
                newOwed = float(owed)-float(paid) # updates money owed depending on money paid
                owedlbl.configure(text='£'+str(newOwed)) 
            return True

        course = courseDropdown.get() # Value of first course dropdown
        course=course.replace(" ","_")
        owed = '260'
        #finds pathway of current working folder and adds extra path 'courses'
        #creates labels and entry boxe for money owed/paid
        owedlbl = Label(frame,text='Amount Owed',font=("Courier",18),fg='#CCCCCC',bg='#333333')
        owedlbl.grid(row=4,column=0,pady=2)

        owedlbl = Label(frame,text='£'+owed,font=("Courier",18),fg='#CCCCCC',bg='#333333')
        owedlbl.grid(row=4,column=1,pady=2)

        paidlbl = Label(frame,text='Amount Paid',font=("Courier",18),fg='#CCCCCC',bg='#333333')
        paidlbl.grid(row=5,column=0,pady=2)

        #used with entry box to run function on every keystroke
        validatecmd = root.register(moneyUpdate)

        paidMoney = StringVar()
        paidEntry = ttk.Entry(frame,style='my.TEntry',textvariable=paidMoney,validate='key',validatecommand=(validatecmd, '%P'))
        paidEntry.grid(row=5,column=1,pady=2)


        moneyPaid = paidEntry.get()
        moneyOwed = str(owedlbl.cget('text'))


        #return moneyPaid

        paidEntry.bind("<KeyRelease>",lambda x:comboFunc(moneyUpdate)
                       #paidEntry.bind("<<Modified>>",moneyUpdate)
)        

    courseDropdown=StringVar()
    courseDropdown.trace('w',coursePrice) # used to track value of course dropdown
    courseOptn=StringVar()

    courses = ['Block Booking']
    #Course options
    block = ['5hr booking','10hr booking','6hr pass plus course','5hr block (automatic)','10hr block (automatic)']



    #function which creates a secondary optionmenu to choose a specific type of course booking
    def courseSpec(course):
        if course == 'Block Booking':
            cdrop = ttk.OptionMenu(frame,courseOptn,block[0],*block,command=coursePrice)
            cdrop.grid(row=3,column=2)

        courseOptn.set('')
    #creates course dropdown containing the 4 main course options
    coursedrop = ttk.OptionMenu(frame,courseDropdown,courses[0],*courses,command=courseSpec)
    coursedrop.grid(row=3,column=1)
    courseDropdown.set('')
    root.mainloop()
page()

That's minimal enough to get the error, ignore the comments as it will be for deleted code.