Debugging Apprise notifications

[mpfl]

I've configured an apprise notification for a particular feed as I want to get a Pushover notification when a new post is made.

Unfortunately, it doesn't work and I'm at a loss when trying to work out where the problem lies. I have tried:

1. Checking the Miniflux logs (set to debug) for any mention of apprise or pover - there is no mention
2. Confirming that the Apprise service URL works using Apprise on the command line

Can anyone recommend any further steps to debug the Apprise integration?