When I do a blind transfer then I want freeswitch to call back the origin who initiated the call.

But I am not able the capture the transfer event?

<condition field="destination_number" expression="^att_xfer$"

<condition field="destination_number" expression="^is_transfer$"

They seem do be ignored by the dialplan. Is there a list what kind of values destionation_number can have besides the called numbers?

I am doing the transfer with a grandstream gxp2140