My friend cannot find multiplayer world but i can see theirs

Whenever i make a multiplayer server my friends cannot see my worlds in the friends section but when they set up a server i can join them normally. I've bought the app and my friends didn't meaning they have transferred me the app that is apk so we can have the same version, is this the cause of this. I am very sure that the version didn't matter bacause previous versions also occured this way. Please let me know soon thx. 1.13.0.2 is the apk version we are now using