Mints a firm quote for one stablecoin swap in the business's Go Account: the provider's all-in rate, the business's swap fee frozen at its current schedule, and the amounts sent and received, until expires_ts. The swap create consumes the quote by id, once. Nothing moves until then.

Every check runs before the quote is stored, and a failed check answers its error code: swap_custody_mode_unsupported, swap_amount_too_small, swap_amount_too_large, movement_limit_exceeded (the swap daily limit), insufficient_balance, swap_provider_balance_unsettled, swap_rate_out_of_bounds, then swap_route_unavailable (503) when the provider cannot quote. Requires kyb_locked, and assets_buy to swap USDC out or assets_sell to swap USDT into USDC. A business whose swap money movement type is off is refused with 403 money_movement_type_disabled.

Requires an Idempotency-Key. A key already used with the same body is refused with 409 duplicate_idempotency_key, and with a different body with 400 idempotency_key_body_mismatch; neither returns the original quote, so keep the quote_id from the first answer. A refused request claims no key and can be sent again.