Setting up an external provider for Zotero's synchronization allows to save more contents on your Zotero without upgrading your Zotero storage.
Register on
pCloud
Open Zotero, go on Edit - Preferences - Sync tab.
Set as url:
webdav.pcloud.com:443
put your pCloud username and password
click on Verify Server, then close.
Note: in case you were using another file synchronization service, go again inside the Sync tab and click on reset - restore to online library