Register an order for shipping-insurance coverage, spending the offer_id returned by a quote. The offer token is single-use, and Mulberry derives the insured value from the order breakdown rather than accepting it from the caller. Re-registering the same external_order_id returns the existing policy instead of creating another.

Payload validation runs before token resolution:

• No Authorization header, invalid body — 400
• No Authorization header, valid body — 401
• Authorization header with an unrecognized token — 401, whatever the body

Mulberry derives the coverage amount rather than accepting it: min(order_items_subtotal - premium, quoted_value) + min(order_shipping + order_tax, quoted_value). Each half is capped at the quoted value independently, so coverage can exceed what you quoted — the ceiling is twice quoted_value. An order_items_subtotal that omits the premium under-insures the order rather than failing, and one at or below the premium is rejected.