Reward Item not showing after completing Day 1 Challange in Errie Office Party Server !!

You should update the title to reflect that it is the "Mojang Office Shirt". I am experiencing the same issue on version 1.21.50. I completed the challenge yesterday afternoon and it has not shown up in my account despite multiple restarts of the game.

Have you checked your headwear? The Day 1 Challenge reward items is Mojang Office cap, not Mojang Office shirt, the information in the sticker book is incorrect.

Oh wow you are correct Keju! Thank you!