Did it remain“undelivered” on the PDA as you couldn’t proceed to get a photo without inputting a date of birth?
If so, and you managed to post just as a silly careless error, a conduct warning seems harsh. To err is human, and a few words about taking much greater care, perhaps looking at labels and PDA before moving the item anywhere near a letterbox, would have sufficed imho. If not, a serious conduct warning might have been appropriate.