Recently in an Adventurers League game the DM prevented my PC from using a magic item because I had not mentioned to the DM before the game that my PC possessed it, but I didn't know I was supposed to mention it. He didn't ask to review my PC's magic items prior to the game, and other DMs I've played with have never asked to review my PC's magic items prior to their games.
By the Adventurers' League rules, must a player tell the DM what magic items the player's character possesses in order for the PC to to benefit from them in that game?
Note : to his defense, he did ask me, in a previous game a couple of weeks ago, about what magic items I had at the time, so I suppose he considered that we were aware that we should tell him of new items, but playing with so many different DMs with different procedures gets confusing over time.
Best Answer
The only official information I found about your question is in the FAQ for the Adventurer's League, page 14, in the chapter Gaining levels between sessions:
So while this suggests the DM and the players should trust each others about magic items, there is no rule in the AL documents stating that a player has to annouce the magic items he possesses.
Also, the magic item you have should be duly recorded on your logsheet :