I can't join my Friend/Multiplayer World

This is the problem with multiplayer

My Minecraft Username:HYREDUser Gamin

I try A lot of Time but still can't join my friend world

My friend say the world are enable multiplayer mode and he invite me but I can't join their world, I don't know why I can't join my version and my friend version are same and I was online...but I can't join, I tried a lot of time!....