If you don't say hello, you will get Hong Kong dollars by default, and if you spend money in countries where dollars are widely used, you will brush dollars by default.

Therefore, in order to save the exchange rate exchange fee, it is generally necessary to say hello to the cashier when swiping the card, so that RMB can be directly consumed.

My card is similar to yours, dual-currency account, UnionPay +visa. Once the cashier made a mistake in swiping the card, the SMS showed that pos spent HK$ xxxx, and then the transaction was cancelled, using UnionPay. SMS shows that the POS machine spent RMB XXXX.