The Rewards cashback bonus is paid automatically on the 1st of each month, for the previous month's trading. It is credited shortly after midnight UTC, which is around 9:00 in Japan, and appears in your Cashback Bonus balance on the trading platform and in Transaction History in the client area, under the Balance History tab, as Bonus.
It is paid only for months in which your trading volume reached the Bronze tier. If you finished a month below Bronze, nothing is paid for that month, and your volume starts again from zero on the 1st.
You can follow each month on the Rewards Program page in the client area, where the payment status shows as accruing while the month is still running, and then as paid, or as below minimum if Bronze wasn't reached. If a payment you were expecting hasn't appeared by the 2nd, contact us through the chat. See What is the Rewards program?
Related: What is the Rewards program? · How to check your Rewards tier · I haven't received my cashback bonus · Bonus and cashback conditions