Chanspy calling from a sip trunk

Is it possible to use chanspy command calling from a SIP trunk, with Asterisk registred to a voip provider??

For example…

in sip.conf:

register => my_user:my_password@my_sip_provider:5060/1221

in extensions.conf:

exten => 1221,1,ChanSpy(SIP)

Then I call my_user registred from Asterisk (by another account on my_sip_provider)
I do some tests but it doesn’t seem to work!!