This is an OLD screenshot but you uncheck the box in the big yellow box below the amount you're contributing and the part where you tell if you're retired or if not, your employer/job/phone number. The box is preprogrammed as checked. It's always said you were agreeing to a weekly/monthly donation if the box was checked.
Problem was/is people not paying attention.
I went through the text messages on my phone, never saw the checkmark option. I could donate through the website. Really not worth rehashing now.