I have a personal account with monthly billing through iTunes. When I log in to the web portal, I don't see an Invite button in the sidebar.
Here's my view of the upper right corner of the page (would be nice if some docs explained what "the sidebar" refers to):
1Password Version: Not Provided
Extension Version: Not Provided
OS Version: Not Provided
Sync Type: Not Provided
Referrer: forum-search:No invite button in sidebar of web portal