I use this in my dialplan before a bridge

...

<action application="set" data="instant_ringback=true"/>
<action application="ring_ready"/>

<action application="tone_detect" data="fax 1100 r +5000 transfer 'receivefax XML features' 1" />

....

but no ring is back to the caller. if I remove tone_detect the ringback is working again.

is anyone knows why ?

Thanks