This means that they likely entered the wrong birthdate previously, by accident. If they enter a birthdate that makes them less than thirteen years old, the number will be blocked from signing up for 24 hours. Even if they change the date and resubmit the form, they will still be blocked for 24 hours. The member can wait a full 24 hours and then text the number again for a new link. If they don't wait 24 hours, the countdown will be reset if they try and submit the form again.
For Example: If you accidentally put in 2020 as the birthdate year the system would identify you as too young and lock you out for 24 hours. After 24 hours, you can text the number again and sign up using the correct date of birth.