This report was made for a member of the community who reported the issue in the Minecraft discord. This issue has also been reported on Reddit: https://www.reddit.com/r/realms/comments/1554ihn/getting_this_error_when_i_try_to_choose_a_realm/

I have recently Bought a Realm, and no matter what name I give it in the "Name" Section when configuring it, it comes up with the error code, "ekm: Realms service error (400/6008) Invalid Realm name". There is no word of this error on Mojang support and all mention of this error is within the last couple of hours, so I believe it is a recent glitch/bug which Mojang has not discovered yet.