Voucher glitch

I was very excited last week to receive 2 emails from Order In with voucher codes for discounts. I wanted to use one of the vouchers last night 15th October (as it expired at 10:00p.m. last night). I placed my order and went to the checkout. I tried 3 or 4 times to enter the voucher code and kept getting an error message saying it was invalid. I called the helpline and was told that that specific code was problematic and couldn't be used. Basically, the voucher was defunct but we were not informed of this via email or the app. Therefore, I was offered a discount that was not usable and was not informed of this issue. Very disappointing...dangling the carrot that turns out not to be a carrot at all!