Your universal link is missing the @instance part at the end, so it tries to redirect to a community called 'plugins' on the instance of whoever clicks on it.
This should work for everyone: /c/plugins@sh.itjust.works
And if it doesn't, see the FAQ in the sidebar here; first search for https://sh.itjust.works/c/plugins on your instance so that it fetches info on the community, then you can click the above link again and it'll work.
That is a pretty recent policy, from the last year or two, it's available in a limited number of countries, and it's a pilot you need to manually apply for. And you still need to pay the fee to Google, it's only reduced by 4%, so instead of 30 it's 26 / instead of 15 it's 11.
More info: Google Play Help Center: Enrolling in the user choice billing pilot