Minecraft Pocket Edition multiplayer bug?

I wanted to play Minecraft (Pocket Edition) with my friend

(we're currently not on the same Wi-Fi, but I can join his world normally)

If he wants to join me, he just says: No connection to the world

I haven't found anything about this on the Internet, only that some of them have the bug or whatever it is.

Please no answers with: yes then just join it's no help. Thanks

here are my settings

Has he set up that friends can join?