When Xbox Live services go down, many players on Xbox One and Microsoft servers start experiencing various errors. These issues usually prevent players from connecting to their ideal game of choice and prevent them from going online to play with their friends or against other players. If a game relies on online services, such as Sea of Thieves or Red Dead Redemption 2, players will encounter several issues.
The only thing you can do is wait. This is all entirely on Microsoft's side, and they will need to figure out what the issue is that brought it down. For those interested in learning more, you can watch the status of the service on the Xbox Live Status page Microsoft manages. The page will contain a variety of updates providing players with valuable information on what is happening and what is being done to help them.
When a problem occurs, there's probably a red "x" next to the service, which also means Microsoft knows about the problem and is trying to fix it. Since the problem is on the platforms side, you will not be able to reset the service or attempt to reactivate it on your side.
You can also follow live updates provided by the Xbox Live support page. They will provide immediate updates regarding anything happening on the Xbox Live status page and any issues they know are occurring.