Now it seems that UnionPay has been decoupled from overseas payment institutions.
A card cannot have both UnionPay and overseas payment functions.
That is, only UnionPay cards are free of charge. Overseas VISA and MASTER cards cannot be used.
For VISA, there is a 1% handling fee for swiping at VISA POS machines. I don’t know how much it is in UnionPay.
It seems that UnionPay cannot be used at VISA.