Invite friends option and permissions menu sometimes does not appear.

This happens because of your connection status and the way the world has been set up. (Enable the world's Multiplayer mode).

but i was on a realm...

In this case, only the realm owner decides who will play. Because he needs to add the players to the access list. O reino era seu?

Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-29007.

Please add a vote and any new information to the main ticket, which will be updated accordingly.

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