Fetches the current exchange rate for a proposed buy or sell transaction.

This endpoint provides a preview of the conversion, including the exchange rate, the equivalent amount in the base currency, and any applicable fees.

Key Rules:

• Charges: Applied only to BUY operations. Sell operations generally do not incur exchange fees.
• Currency: All fees and base currency amounts are calculated and presented in the account's base currency.
• This API should be called to retrieve live rates and charge estimates before initiating a currency lock or execution.