Zotero integration to LibreOffice

Hello, guys!

I’ve installed both Zotero and LibreOffice from Flatpack on my Debian 9. These apps are just awesome! It’s a great pleasure to use these apps, really. However, there is one very important issue about the installation of Zotero plugin extension to LibreOffice. I can’t find a way neither from the “Zotero LibreOffice Plugin Installation” in Zotero preferences, nor from the “Tools/Extension Manager” from LibreOffice. Respective folders with necessary files and directories could not be seen from the both managers for extension installation. And when I click directly on Zotero_OpenOffice_Integration.oxt file, it just prints “/var/lib/flatpak/app/org.zotero.Zotero/x86_64/stable/54c8918688968ff6af8c2a4fb76f3f3ed1aa3fd3698f159d516eb264a0dabd9c/files/share/zotero/extensions/zoteroOpenOfficeIntegration@zotero.org/install/Zotero_OpenOffice_Integration.oxt does not exist”.
Who knows the issue?