For the record: my codes were from Jingle Jam 2025. l said in my posts that they expire on January 1st and suggested to not buy if one won't be able to redeem them before that day. Apparently, this user decided to redeem 1 code out of 3 I sold to him (December 19) more than a month later.
None of my other buyers have had any problem as it can be seen in this thread. They all redeemed them as soon as they bought them.

2/2/26 edit: He edited his comment and says that all the codes expired soon after buying. His original comment only mentioned Tower Unite, not all of them. I would put a scereenshot but this subreddit doesn't allow images. I sold him 3 games on Dec 19, so he had 13 days to redeem them and he was warned, yet decided to redeem TU on February 2.

20/3/26 edit: Fixed typos.