One of your biggest and best customers calls to complain about the last batch of blank cards you sold them.
As their integrator, you order all cards for their system to make sure details like card numbers, facility codes, and credential type are compatible.
When you order cards for them, one of your techs hand-delivers them onsite and spends some time 'pre-enrolling' them into they client's system. Your tech scans each card at a reader in the system to activate it, so then all your client needs to do is assign a name, access schedule, and print them as needed. (They do this part on their own, and have their own printer.)
They are calling because the last batch you sold them do not read at all at any reader in their system. Once they print and hole punch the card, they appear dead to any reader (no beeps or LEDs flash)... even the reader your tech used to enroll them into the system just ignores them.
Your customer thinks you must have ordered the wrong cards, but your tech swears everything worked just fine when he delivered them. You make a drive out to the customer's HQ and ask to look at a card. You immediately spot the problem:
What is the problem?