Should somebody from the USA have their number listed like so:?
1 + area code + number ?
(Edit - I managed to get into my account again using the Authenticator app and I will make sure that I have my phone number listed in the correct format, should I ever need to reset my 2FA in the future.)
Yes. We obviously need to know which country to send the SMS to so including the country code is mandatory.
I assumed the "Only use numbers" referred to the use of any dashes or spaces but does it also mean to leave out the + sign that an international number usually starts with?