If you're experiencing some issues with matchmaking on your Xbox One or Xbox 360, you're not alone. According to the Xbox Live Service Status page, matchmaking on both consoles is currently down for some.
Having trouble creating or joining multiplayer matches? Can't join parties, send party invites or view the activity of users on your Friends list? We're aware of these issues, and our engineers are working hard to reach a solution ASAP! Thanks for your patience, Xbox members. We'll keep you posted as soon as we know more.
The outage looks to have started around 45 minutes ago (at the time of this writing), but Microsoft is on it, and things should return to normal relatively soon. If you want to keep track of the outage status, you can follow along at the Xbox Live Status page for more.
Update: Looks like everything is back to normal. Carry on, folks!
Source: Xbox Live Service Status