I'm not sure you understood chipbennett's question. Have you received a NEW certificate since 2/1/24, which was only 9 days ago? This certificate wouldn't expire until February of 2025. The rule changes do not apply to certificates you already had in your account before 2/1/24. Somebody found language to that effect on DL's website, maybe in the T&Cs, but I'm too lazy to try to find it.

If you did receive a new cert in the last 9 days, then I'd guess that DL's systems haven't been updated to accommodate it yet.

I tried to book a flight to Hawaii with an older certificate and got the same error you did. I have to wait until I earn my next certificate, which is in May.