sudo /etc/init.d/apache2 restart:
[....] Restarting apache2 (via systemctl): apache2.serviceJob for apache2.service failed because the control process exited with error code.
See "systemctl status apache2.service" and "journalctl -xe" for details.
 failed!

systemctl status apache2.service:
● apache2.service - The Apache HTTP Server
   Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Thu 2018-08-23 23:23:12 CEST; 46min ago
  Process: 24928 ExecStop=/usr/sbin/apachectl stop (code=exited, status=1/FAILURE)
  Process: 25127 ExecStart=/usr/sbin/apachectl start (code=exited, status=1/FAILURE)
 Main PID: 22761 (code=exited, status=0/SUCCESS)

Aug 23 23:23:12 vserver4.blackfirefly.org systemd[1]: Starting The Apache HTTP Server...
Aug 23 23:23:12 vserver4.blackfirefly.org apachectl[25127]: AH00526: Syntax error on line 11 of /home/easywi-web/sites-enabled/easywi_
Aug 23 23:23:12 vserver4.blackfirefly.org apachectl[25127]: Invalid command 'Header', perhaps misspelled or defined by a module not in
Aug 23 23:23:12 vserver4.blackfirefly.org apachectl[25127]: Action 'start' failed.
Aug 23 23:23:12 vserver4.blackfirefly.org apachectl[25127]: The Apache error log may have more information.
Aug 23 23:23:12 vserver4.blackfirefly.org systemd[1]: apache2.service: Control process exited, code=exited status=1
Aug 23 23:23:12 vserver4.blackfirefly.org systemd[1]: Failed to start The Apache HTTP Server.
Aug 23 23:23:12 vserver4.blackfirefly.org systemd[1]: apache2.service: Unit entered failed state.
Aug 23 23:23:12 vserver4.blackfirefly.org systemd[1]: apache2.service: Failed with result 'exit-code'.