What problem does the man mention?

W: Hello. My name is Betsy Peterkin, and I am calling about a gift voucher which I tried to redeem at your store today.
M: Hi, Ms. Peterkin. I’m the store manager. How can I assist you?
W: I’m phoning to let you know how dissatisfied I am with your business. This morning, I presented my voucher to the cashier, but she told me it had expired. This is confusing as your Web site states that all vouchers are valid until December 31.
M: I’m sorry for the misunderstanding. Unfortunately, that information was incorrect, and we
have already changed it. The vouchers have serial numbers on them, and these serial numbers indicate when the voucher expires.
W: Oh, I see. Yes, mine has the serial number 139. What does this mean? Has it expired?
M: I’m afraid it has, but I’d be happy to issue you a new voucher the next time you are in our store. You can exchange your old one. Sorry for the inconvenience.