As mentioned you need to update the server. Servers with the Default License file expiration date of today are older than version 3.10.0 (which updates the default license file to 1st of July 2020). I feel this is a method the TS development team used to protect users for un-updated servers that may have security issues for the users. But suggest updating to the current stable.
For information on updating your server please see: Update / Upgrade a TS3 server
