The vast majority of times that the customer "does everything right", but my website "refuses to let them check out", and/or gives them error messages that do not appear ANYWHERE IN THE SOURCE CODE ... they are elderly.
If you cater to them, they will be more loyal and spend more than most other demographics.
And truly, if you make your product usable by the elderly you also remove a lot of barriers for other groups and reduce the friction on the merely busy.
I had something similar happen once, several customer service reps insisted that a message I was getting was entirely impossible: it told me I needed to buy competitor's prepaid card instead of theirs. I'd just assumed they had a deal with that competitor for prepaid card distribution.
They fixed the message soon after I ended the call, but when I called back later they still didn't believe me. Finally I pointed out that when they fixed the message they forgot to change it from their competitor's prepaid card number format. Then they finally credited my account.