I cannot connect to friends worlds with xbox live

So my friend invited me to his mcpe world. I click accept and it opens up windows 10 edition beta. I wait for me to enter my friends world but after 5 mins of waiting I realize that I'm not entering his world. This is not the first time its happened I really like mcpe but please give me tips!
Just to see if this helps I'm running on a nextbook flexx 8.9