Hello,
I've got Ubuntu 20.04, and when I try to Add/Edit a cite, appears this error:
LibreOffice could not communicate with Zotero. Please ensure Zotero is open and set to an online state and try again."

I tried the following:

Re-download Zotero.
Reinstall LibreOffice
Reinstall Plugin
Disable the firewall
Check if the plugin is enabled

And I don't know what else to do. Could some one help me, please..