It's ${EXTEN} NOT {EXTEN}
>
> Mar 29 17:44:18 NOTICE[11502]: chan_iax2.c:6794 socket_read: Rejected
> connect attempt from iax.providers.server.net, who was trying to reach
> '{EXTEN}@'
>
> Tx-Frame Retry[000] -- OSeqno: 000 ISeqno: 001 Type: IAX Subclass:
> REJECT