Device Account Number

I have been having the same problem as many others, as I have read about in the thread "After update Apple Pay says my card is expiring but it is not". Seems that the best bet is to enter a different card, remove the card that has not expired, then reenter it, then delete the different card I just added. I think it must be important to enter the info manually, because when I take a picture of my card, it has only two digits for the year. Getting ready to try this, but in the meantime, I noticed that in 'Manage Payments', It lists a Device Account Number. What is this referring to? I don't recognize this number and can't find it anywhere else.