This integration selects new and updated G Suite contacts and imports them to Zoho Books. It does not create duplicates; if a contact with such primary email already exists in Zoho Books, the integration updates it instead of creating a new one.
This integration also imports data from the OtherContacts object, which stores information about addressees you have emailed but haven't added as a contact. Note that for such addressees, only the first and last names are imported, and not the other data.
Note: It does not import pre-existing G Suite contacts to Zoho Books unless they are updated in G Suite.