Attended transfer feature codes

Hello,

I am having difficulty with Feature Codes for Attended Transfer.
FreePBX 14.0.1.14

What works:

  1. Incoming call (A) is answered by B
  2. B presses *2 and calls C, C picks up. A is now on hold
  3. At this stage, B pressing *2 joins A & C. B pressing *3 makes a 3-way conference call between A, B &C.

What doesn’t work:
B cannot disconnect from C and get back to the call from A. If C hangs up on B, B gets back to A.
But I don’t know how B can get back to A without C’s involvement. ** does not work for me.

This Asterisk page (https://wiki.asterisk.org/wiki/display/AST/Feature+Code+Call+Transfers) suggests
atxferabort=*3 (or some other feature code…)
to abort an attended transfer.

However placing this line in
/etc/asterisk/features_general_custom.conf
or
/etc/asterisk/features_featuremap_custom.conf
does not work. The *3 3-way code remains in effect.

Any ideas?
It would be great to know where the definition of *3 is coming from FreePBX. It does not appear in Feature Code Admin.
It would also be great to be able to define the atxferabort Feature code and use it.

Thanks,

Jerry.