UpdateLeadCustomFields

Update (upsert) custom fields on a lead in a campaign. Keys are field names, values are field values.

• If a field exists: its value is updated.
• If a field does not exist: it is created.
• If the value is null or an empty string: the field is deleted.

Up to 100 custom fields per request. Field names max 128 chars, values max 2048 chars. leadMemberIdOrUrl accepts a LinkedIn member id or a (URL-encoded) profile URL. Returns the final state of all custom fields on the lead (the listId is the campaign’s underlying lead list).