clean stale sessions with radzap?

[YvesDM <ydmlog@gmail.com>]

I use FR + mysql
I try to clean some stale sessions from NAS's with dynamic ip's.
I 'm logged in on the server and use radzap this way:
radius1:~# radzap
Usage: radzap [options] server[:port] secret
So i try:
radius1:~# radzap -u john localhost:1812 mysecret

But this doesn't seem to be the right way?

tnx yves