Are the servers going to be up anytime soon?
The issue with Halo 5 was related to Xbox Live having service issues:
https://www.halowaypoint.com/en-us/forums/6e35355aecdf4fd0acdaee3cc4156fd4/topics/xbox-live-outage-19-march-2018/241fd4cb-c028-4260-b0e7-ca95ab7ddf00/posts