Changes the named contacts at once: names, phone, country, time zone, language, custom fields, subscription status, tags added or removed, a new e-mail. Each item names a contact by id; to find one by its address, use list_contacts with email. Up to 100 items per call, the page size of list_contacts; one contact is a list of one.

The answer reports every item in the order given: updated, unchanged (nothing to change, nothing written) or failed with a reason; one failed item writes nothing of its own and does not stop the others.

A field left out is kept; null clears first_name, last_name, phone, country, timezone and language; fields are keyed by field ids from list_contact_fields, merged by key, and null removes a value. Tags go by name, compared without case: add_tags adds them and creates a tag the site does not have, remove_tags takes them off; tags not named stay. changed names the fields that were written.

Status: subscribed is allowed from unsubscribed, and subscribes again a contact who opted out, as the admin does; leave status out to keep what the contact chose. unsubscribed is allowed from subscribed or from awaiting double opt-in. A bounced contact changes status only with a new e-mail, and a contact awaiting double opt-in is never subscribed here. A status change that is not allowed does not stop the rest: the other fields are written and reason says why.

A bounced contact with a new e-mail becomes unsubscribed unless status says otherwise; its links to sent e-mails are dropped, email_stats start over and the new address is checked. An item that changes nothing keeps updated_at.