Create a new shopping cart on Kifly. **For network (cross-seller) tokens you MUST pass `seller_handle`** — each cart is bound to exactly one seller. Get the handle from search_products results (every item's `kifly:seller` IS the handle in network results) or get_seller. Seller-scoped tokens may omit the handle — their own seller is implicit. Returns a cart_id to use with add_to_cart and checkout. The response's `seller.kifly_purchasable` (and `seller.fulfillment`) tells you upfront whether this seller can complete a real Kifly checkout — `false`/`"external"` means directory-tier: checkout will hand off to the seller's own site instead of charging, so present the flow as a referral, not a purchase. Cart-building still works either way (needed to generate the handoff's per-product links), and the same flag rides every add_to_cart/get_cart response on this cart too.
Connector