I ran into the same issue and did some digging. The Debian package for ZoneMinder lacks this folder: /usr/share/zoneminder/www/api/app/Plugin
It is part of the original ZoneMinder release: https://github.com/ZoneMinder/ZoneMinder/tree/release-1.30.4/web/api/app/Plugin The Crud plugin references the Crud GitHub repository in a specific version. The Debian package maintainer probably missed that referenced Git repository. Until the zoneminder package gets fixed, you can work around this by downloading the Crud plugin from here: https://github.com/FriendsOfCake/crud/tree/c3976f1478c681b0bbc132ec3a3e82c3984eeed5 Copy all files to /usr/share/zoneminder/www/api/app/Plugin/Crud (must be created first). Enjoy a working API.
