test.rb

require "selenium-webdriver"

driver = Selenium::WebDriver.for :chrome
driver.get('https://www.soul-cycle.com')

# login as your user - replace username and password
driver.find_element(:class, "log-in").click
sleep 1
driver.find_element(:name, "email").send_keys("chromedriver@test.com")
driver.find_element(:name, "password").send_keys("tester")
driver.find_element(:name, "submit").click
sleep 1

# go to the account info/billing page
driver.get('https://www.soul-cycle.com/me/account/payment/')

# expiration month element
dropdown = driver.find_element(:id, "dk_container_frm-cc_month").find_element(:class, "dk_toggle")
dropdown.click
sleep 1

# this throws the cannot focus element error
5.times { dropdown.send_keys(:arrow_down) }
dropdown.send_keys(:enter)