我尝试制作一个随机回答kahoot的脚本，一切正常，但当脚本必须单击“下一步”按钮时，我得到了这个error:'selenium.common.exceptions.InvalidSelectorException: Message: invalid selector: An invalid or illegal selector was specified'。我尝试搜索这个错误，但没有显示与我的脚本相关的任何内容。

import random
from selenium import webdriver
driver=webdriver.Firefox()
driver.get("kahoot link")
choices= ['//*[@id="challenge-game-router"]/main/div[2]/div[1]/span', '//*[@id="challenge-game-router"]/main/div[2]/div[2]/span', '//*[@id="challenge-game-router"]/main/div[2]/div[3]', '//*[@id="challenge-game-router"]/main/div[2]/div[4]']
try:
    sleep(5)
    nickname= driver.find_element_by_name('nickname')
    nickname.send_keys(username)
    enter = driver.find_element_by_xpath('//*[@id="challenge-game-router"]/main/section/div[1]/form/button').click()
finally:
    pass

for c in range(0, 3):
    try:
        driver.implicitly_wait(20)
        choice = driver.find_element_by_xpath(random.choice(choices))
        choice.click()
        driver.implicitly_wait(20)
        next = driver.find_element_by_xpath('/html/body/div/div/div/div/main/button')
        next.click()
    finally:
        pass