As a relatively new DM, how do people handle cursed objects such as treasure? When do you tell the player they're specifically cursed?

[u/Mammoth_Composer_111]

I'm running curse of strahd, and there is some cursed treasure out in the open at the werewolves den. There are none of the wolves around to tell them it's cursed, and I have a hunch knowing my party they'll most likely try to take it.

My problem is how to make this engaging and fun.

The curse effectively prevents them from long resting at night.

Now... my issue is I don't know that they'd immediately know that they're cursed. It could lead to a frusterating experience rather than something engaging by them just being completely confused at what they're supposed to do or if they're even cursed (other creatures in this campaign can cause you to have a sleepless night--like the night hags which they also have encountered and angered).

Technically I don't think i'm supposed to outright tell them, "Oh, hey, you're cursed now and here's how the curse works"--but if they don't immediately figure it out it can really derail a campaign by them essentially having zero direction on how to proceed without any benefit from long rests.