Need help with bwdpi command

[leoxp9515]

I was trying to get traffic status through bwdpi command. Here's what I get from console:

xxxx@TUF-AX4200Q-B2FA:/tmp/home/root# bwdpi
Usage :
bwdpi [iqos/qosd/wrs] [start/stop/restart]
bwdpi dc [start/stop/restart] [ptah]
bwdpi stat -m [mode] -n [name] -u [dura] -d [date]
bwpdi app [0/1]
bwpdi device
bwpdi device_info -m [MAC] -p [IP]
bwpdi get_vp [0/2]
bwpdi wrs_url
bwpdi checksize path size
bwpdi get_app_patrol
bwpdi get_anomaly [0/2]
xxxx@TUF-AX4200Q-B2FA:/tmp/home/root# bwdpi stat -m traffic -u realtime
You must input option mode(m) / dura(u), if lost any one, it can't output any information

According to https://github.com/RMerl/asuswrt-merlin.ng/blob/master/release/src/router/www/getTraffic.asp#L3
and some reverse engineering on libbwdpi.so:

The message "You must input option mode(m) / dura(u)" only appears when mode or dura is null. That makes me confused because I already provided mode and dura (bwdpi stat -m traffic -u realtime).
Anyone knows what's wrong?