Originally Posted by
WR Cage
Looks like you are flying to the USA from a pre-clearance airport. In these instances US CBP will not accept electronic BP so you must have a physical paper for them to add their stamp or otherwise review and markup. Also all cellphones need to be stowed while in CBP and all bluetooth handsets removed from your ear.
ETA: Missed AC681 comment which beat me to the punch.
Ahhhhhh
Thank you guys. That makes more sense now.