It doesn't have to be much. It can come with an explanation. If they are learning English, it's useful to know for the anglophone world ghosting (in many situations) is considered extremely rude.
I think Japanese people would be very receptive to this information and the $ incentive to let them know you're serious about it.
I think Japanese people would be very receptive to this information and the $ incentive to let them know you're serious about it.