I don't see the join party option

How about instead of trying to get them to join you, you join their games instead?

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Send a message asking if you can take part or see if the Join Session in Progress option is available. If they are in a Party then check if the join option is there.

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In short don't wait for them to come to you, go to them.

Has some of the party functionality been removed in the beta? I still see the option to start a party, but when I click on the gamertag of a friend that I know is in a party, I no longer see the details of the party (the names of the other people in it),
nor do I get an option to join it. I can only start my own party.

So GG if you invite me and i don't join yet i am in a party then you will join my party? thing is you see is if i don't join you and i am in a party and i don't invite you then its mainly because the person i am in a party with wants it to stay as it is,
it is nothing personal my friend but i have a friend who likes to game just me and him.

There could be many reasons for that, but first please elaborate, are you trying to join her through the friend list?, do you see the join option when doing so? or you can join and then see an error message on the party?

Hi i have the same problem can not join other people's party's also people can not join mine. and just a bit feed back on the xbox one the party system has always been bad the 360 was just right easy to use and smooth 1 of my biggest misses from the 360
is the party option and i don't like how you can not see who you just played online without going back to dashboard just feels a bit messy ATM and confusing to the average gamer