I explain, when I go to the world settings to be able to play with friends, I obviously activate the multiplayer but when I enter the world the multiplayer is disabled and I can't play with anyone. Could you help me with a way to solve the problem? Thank you

Gotcha! You can't change the multiplayer settings while you're still playing on a world. In order to enable Multiplayer, you have to back out and hit the pencil icon next to the world to bring up the Edit options. This should let you enable Multiplayer. ^LK