HRESULT XUserAddByIdWithUiAsync(  
         uint64_t userId,  
         XAsyncBlock* async  
)  

// Assumptions:
// 1. The game has previously registered for this callback using XGameInviteRegisterForEvent
// 2. The game has function: uint64_t GetXuidFromInviteUri(const char* inviteUri)
// 3. There is already a global task queue, g_GlobalQueue
 
void MyGameInviteEventCallback(void* context, const char* inviteUri)
{
   XAsyncBlock* asyncBlock = new XAsyncBlock();
   asyncBlock->queue = g_GlobalQueue;
   asyncBlock->callback = [](XAsyncBlock* ab)
   {
      XUserHandle userHandle;
      if(SUCCEEDED(XUserAddByIdWithUiResult(ab, &userHandle)))
      {
         // Copy this XUserHandle to some location that the game will use later or
         // Do whatever actions you want with this user

         XUserCloseHandle(userHandle);
      }
      else
      {
         // Since you didn't successfully add the user, setup your game state so that 
         // you are in a good place, likely a start menu
      }
      delete ab;
   }

   
   if(FAILED(XUserAddByIdWithUiAysnc(GetXuidFromInviteUri(inviteUri), asyncBlock)))
   {
      delete asyncBlock;
   }
}