Are you receiving the error "the authentication servers are currently not reachable" when trying to join your Minecraft server? This is likely not an issue with your Minecraft server.
This issue is caused by the authentication servers that Mojang host being unavailable. This can happen for a few different reasons, however it is usually because of scheduled maintenance or some sort of bug on their side.
How long will this issue last for?
This kind of issue happens quite infrequently and luckily tends to only last for a maximum of 15 minutes.
Can I bypass the authentication servers?
Yes - but we strongly advice against this. If you would like to disable the lookup for authentication on your server (which will allow anyone to login as your account) then follow the instructions in this article: https://serverflex.io/help/article/insecure-mode-on-minecraft-server
What else could this be?
This could be a network issue on your server. If your server is not able to access the global internet (either for DNS lookup or connecting to the auth servers) then you may receive this message.