Multiplayer world won't load

I keep trying to join my friends world. When I go to the friends tab and tap on his world to join it starts loading but gets stuck loading on "locating server" indefinitely. On his side it shows me in the world even though on my side it just keeps loading. Then, if I press cancel, it briefly says "Generating world" then "done!" (Like I've loaded in the world) before just sending back to the friends tab! I've tried waiting a long time, but it never loads.