When I try to open Perusall from my LMS, I get the error message "app.perusall.com refused to connect"

Your LMS may be attempting to open Perusall in a "frame" (i.e., inside a box within your LMS, rather than in its own tab or window). For security reasons, Perusall prevents itself from being opened in a frame. There should be a setting in your LMS to open Perusall in a new tab or window instead; enable that setting, then try to launch Perusall again.