My survival world won't switch to multiplayer

I created a world to play with my long distance friend in survival. I must have switched multiplayer off so he wouldn't join but I want him to play it with me now. I tried switching the settings to multiplayer from the edit button before I open the world. When I do tap play, in the game settings it has multiplayer off still. Ive tried it a bunch of times and I'm not sure if it's a bug or what. I really want to play this specific world with him. Please help! I even tried to make a copy and play it through that but for some reason when I'm in the game, it says multiplayer is off.