Requests a real-time FX quote for a Card Account (CA) top-up. This is the first step in a two-step process (Quote → Trade) that guarantees a locked exchange rate.

• Currencies: The payment currency must be specified, while the receiving currency is always fixed to USD.
• Quote Generation: A quoteId is generated only if the payment amount is provided.
• Entity Binding: The generated quote is strictly bound to the requesting entity; the subsequent trade must be executed by the exact same entity.
• Note: For instant Crypto Wallet to Card Account transfers (without FX locked rates), please use POST /crypto-wallet/transfer.