Blind Transfer Fails - silently, no cli output

Phone A calls phone B

Phone B types:

transfer > blind > phone C’s number > send

Disconnect, with no CLI output to shed light on why it is having trouble.

sip.conf
calllimit=20

(here the call from A to B connects)

== Using SIP RTP CoS mark 5
– Executing [9435@from-sip:1] Answer(“SIP/9285-00000004”, “”) in new stack
– Executing [9435@from-sip:2] Macro(“SIP/9285-00000004”, “stdexten,9435,sip/9435”) in new stack
– Executing [s@macro-stdexten:1] Answer(“SIP/9285-00000004”, “”) in new stack
– Executing [s@macro-stdexten:2] NoOp(“SIP/9285-00000004”, “Beginning stdexten Macro”) in new stack
– Executing [s@macro-stdexten:3] Set(“SIP/9285-00000004”, “dynext=”) in new stack
– Executing [s@macro-stdexten:4] NoOp(“SIP/9285-00000004”, “callerid: 9285”) in new stack
– Executing [s@macro-stdexten:5] NoOp(“SIP/9285-00000004”, “”) in new stack
– Executing [s@macro-stdexten:6] NoOp(“SIP/9285-00000004”, “0”) in new stack
– Executing [s@macro-stdexten:7] GotoIf(“SIP/9285-00000004”, “0?s,100”) in new stack
– Executing [s@macro-stdexten:8] GotoIf(“SIP/9285-00000004”, “0?s,100”) in new stack
– Executing [s@macro-stdexten:9] GotoIf(“SIP/9285-00000004”, “0?s,100”) in new stack
– Executing [s@macro-stdexten:10] GotoIf(“SIP/9285-00000004”, “0?s,200”) in new stack
– Executing [s@macro-stdexten:11] GotoIf(“SIP/9285-00000004”, “1?s,300”) in new stack
– Goto (macro-stdexten,s,300)
– Executing [s@macro-stdexten:300] Set(“SIP/9285-00000004”, “dynext=9435”) in new stack
– Executing [s@macro-stdexten:301] Goto(“SIP/9285-00000004”, “dial”) in new stack
– Goto (macro-stdexten,s,12)
– Executing [s@macro-stdexten:12] Dial(“SIP/9285-00000004”, “SIP/9435,20”) in new stack
== Using SIP RTP CoS mark 5
– Called 9435
– SIP/9435-00000005 is ringing
– SIP/9435-00000005 answered SIP/9285-00000004
– Native bridging SIP/9285-00000004 and SIP/9435-00000005
– Started music on hold, class ‘default’, on SIP/9285-00000004

( we’ve hit transfer, blind and the number, music on hold is playing now as expected)

(send is pressed, then boom it goes down)
/

-- Stopped music on hold on SIP/9285-00000004

== Spawn extension (from-sip, 9254, 1) exited non-zero on ‘SIP/9285-00000004’ in macro ‘stdexten’
== Spawn extension (from-sip, 9254, 1) exited non-zero on ‘SIP/9285-00000004’

Why is this failing, and how to wrench it into a working status?

Please provide a SIP trace including the REFER method from the phone and all the Asterisk responses.