With reference to [this][1], we might need to run the following after configuring systemctl.

 sudo systemctl daemon-reload


And we should have a header in the script like [below][2].

 ### BEGIN INIT INFO
 # Provides: scriptname
 # Required-Start: 
 # Required-Stop: 
 # Default-Start: 2 3 4 5
 # Default-Stop: 0 1 6
 # Short-Description: Start daemon at boot time
 # Description: Enable service provided by daemon.
 ### END INIT INFO


 [1]: https://unix.stackexchange.com/a/364787/270935
 [2]: https://wiki.debian.org/LSBInitScripts