I want to spy on a dedicated extension,
the following is in /etc/asterisk/extensions_additional.conf

include => chanspy-custom
exten => 501**,1,Chanspy(501)
exten => 501**,n,Hangup
exten => 502**,1,Chanspy(502)
exten => 502**,n,Hangup
exten => 506**,1,Chanspy(506)
exten => 506**,n,Hangup

while there is a call with 507, i dial “507**”, the following happens:

-- Executing ChanSpy("SIP/502-09f19e20", "507") in new stack
-- Playing 'beep' (language 'en')
-- Playing 'beep' (language 'en')

I just hear beep, but there is no RTP to hear.

Any thoughts please with examples to spy on a dedicated extension, and is there
a way to toggle between the channels while spying.