I don't know how it's set in OJS 3, but there needs to be an adjustment to OJS 2.x translation for the admin site settings section, as there is no longer a PKP Harvester as there was before.
What we have now, if I'm not mistaken, is the PKP PLN, which is an individual journal registration, by Journal Managers.
The content at admin site settings must be changed to something else, or there must be a redirect somewhere...
Register Site for Indexing (Metadata Harvesting)
To have the contents of all journals hosted on this site indexed within a globally distributed system of research databases, register your site's URL with the Public Knowledge Project metadata harvester. This tool collects the metadata from each indexed item in this journal, enabling accurate and collective searching among the research sites that adhere to the Open Archives Initiative Protocol for Metadata Harvesting.
Click here and enter http://siteurl/index under Site URL, and http://siteurl/oai under Base URL for OAI Archive.
Note that the OAI interface can be disabled for this site by editing the OJS system configuration. Future versions of OJS will allow the OAI interface to be enabled or disabled for individual journals within the site.