Downlink RX Window for RAK7431

Hi, currently I have issue on RAK7431 downlink messages. The downlink message only able to receive after an uplink message sent to the gateway. Is there any way to make it listen to the downlink message all the time?

Just for the information:
join mode= OTAA
region AS923
Class C
PingNb is 128
confirm=1
ADR disabled
LPTP = 0
Data Rate 4
DutyCycle = 0

That is the setting for my RAK7431 and looking for the support, Thanks.