how do i accept sot invites on windows?

The way we've been doing it is to go through the Xbox app. Click on the friend who opened the lobby and then in the center of the app you'll have the option to join them, which gets you into their lobby. Notifications are on for us, but invites seem to just die in the water and never reach the other person. I blame Microsoft, Steam would have been the better route to take but such is corporate greed.