SIP to SIP music on hold

Hi,
I have problems in configuring music on hold between SIP clients: if I dial
from an iax to a sip and then the iax place the call on hold, then the music
starts. If the sip client places the call on hold, the music does not start
and nothing is reported by the Asterisk console. I think it may depend on
the sip.conf configuration, but I couldn’t find docs about this.

Currently I’m using madplay for music, and I have configured the
musiconhold.conf with this setting

[classes]

default => custom:/var/lib/asterisk/mohmp3/,/usr/local/bin/madplay --mono -R
8000 -A -20 --output=raw:-

Thanks

Post the debug of an example call (sip debug peer xxxx).