Managed to find some info to get pushover notifications working.
The templates for the messages used by this are in /opt/traccar/templates/short/
In traccar.xml file you can add the following lines, these are mandatory;
<entry key='notificator.types'>web,mail,pushover</entry>
<entry key='notificator.pushover.token'>YOUR-APP-TOKEN</entry>
<entry key='notificator.pushover.user'>YOUR-USER-TOKEN</entry>
A couple optional fields you can add;
<entry key='notificator.pushover.title'>Optional title for notifications</entry>
<entry key='notificator.pushover.device'>myiPhone10, myiMac</entry>
Release notes for Traccar 4.9 lists support for Pushover notifications, where can I find documentation on enabling/configuring pushover notifications?