Create and update items in an Iterable catalog via the Catalog Items API

Steps

1. Obtain an Iterable API key from the project settings and include it as an Api-Key header on all requests.
2. Create or replace a catalog item by sending PUT /api/catalogs/{catalogName}/items/{itemId} with a JSON body containing the item's field values — this creates the item if it does not exist or replaces it entirely if it does.
3. To make a partial update to an existing item without replacing all fields, use PATCH /api/catalogs/{catalogName}/items/{itemId} with only the fields you want to modify.
4. Verify the item was written by sending GET /api/catalogs/{catalogName}/items/{itemId} and confirming the response matches the expected field values.
5. To insert many items at once, use the bulk upsert endpoint if available for your plan, or loop PUT calls — be aware that as of late 2025, API calls that include the key in the query string rather than the header are subject to stricter rate limiting.