Hi All,
I know its on the roadmap, however i have these working since pushover created webhooks.
Create a new notification via mattermost, for the url use the one pushover gives you when you create the webhook ie https:// http://()api(.)pushover(.)net/1/webhooks/w4y2wzp6h5aXXXXXXXXX.json and for the username i just used TrueNas(can be anything)
then in pushover for title selector use {{username}} and body use {{text}}
hope that helps! i know its helped me as i hated having to use SMTP alerts
Cheers