Xbox is saying that my friend needs to buy his game again after he already bought it.

Your friend will have to contact Xbox Live support for this issue

Had this issue too, my friend just logged in after buying the game and he already had an account. He logged in to his old existing account and it automatically changed his name too. It's stupid

Hypothetically speaking, let's say a friend of mine comes over and logs in to his XBL account from my Xbox One. Since he doesn't already have an Xbox One but plans to get one in a couple weeks, would that set my console as his home console? So when he buys
his, goes home and buys a game, would I be able to download it?

When he opens the game it goes to demo mode.It said that he has to buy the game again but he already bought it. he is connected to xbox live when he attempts. he did buy the game on the the console he is trying to play it on.

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Weird thing is Both myself and a friend both played the demo. Last night we were both playing the main game and were discussing this very thing.

In my game the car was not in my garage after accepting the gift in the messages.

In my friends game the GT was in his garage.

I went and bought the car for 250,000 achievement unlocked

He still didnt have the cheevo but had the car, he had to buy it again anyway to get the cheevo, but like Pkvas said he can sell his for half price. No biggy though it was cheap enough.