How to run systemd timer every 30 seconds

The syntax to run a systemd timer every 30 seconds is:

OnCalendar=*-*-* *:*:00,30

i.e. run on the first (00) and 30th second of every minute.

If this post helped you, please consider buying me a coffee or donating via PayPal to support research & publishing of new posts on TechOverflow