Create a Shippo customs declaration object and attach it to an international shipment to generate compliant customs paperwork

Steps

1. Create one or more Customs Items describing each product being shipped: description, quantity, value, weight, origin country, and tariff/HS code if available.
2. POST to the Customs Declarations endpoint with contents_type, certify, certify_signer, eel_pfc, and incoterm fields, plus either inline items or references to previously created Customs Item object_ids.
3. Include the returned customs_declaration object_id in your Shipment creation call alongside the standard address_from/address_to/parcel fields for an international shipment.
4. Retrieve Rates for the shipment as usual, then purchase the label/transaction — Shippo generates the necessary customs forms (e.g., CN22/CN23 or commercial invoice, depending on carrier and value) from the declaration data.
5. Verify the generated label/customs documents before handoff to the carrier, confirming declared values and HS codes match your actual commercial invoice to avoid customs holds.