Sorry for the slow response, I only just saw this question.
Version 0.6.2 released on 14 October 2019 is actually compatible with Jira 8.7. I've updated the Marketplace entry to reflect this; previously it only claimed compatibility up to Jira 8.5 (because that was the latest Jira release at the time). So you can now install the app into Jira 8.7 and earlier via UPM's "Find new apps" page:
Previously you could install the app into Jira 8.7, but you had to download its JAR file from Marketplace onto your file system, then upload it via UPM's "Manage apps" page: