I'd like to get FreshRSS working with this tool:

https://chrome.google.com/webstore/detail/rss-subscription-extensio/nlbjncdgjeocebhnmkbbbdekmmmcbfjd

One of the things required to configure it to work with FreshRSS is a URL for subscriptions as indicated in the image below:

What URL beyond https://myfreshrss.example/p/i/ to make this work?