IAX config

Hello; I’m trying to connect to asterisk remotely using a iax client (zoiper).
I’m getting the following error when I try to register:
No registration for peer ‘1001’ (from 173.x.x.x)

this is my config:
iax.conf

[general]
autokill=yes
[idefisk]
type=friend
host=dynamic
context=phones

__________________________________________________extensions.conf

[globals]

[general]

[default]
exten => s,1,Verbose(1|Unrouted call handler)
exten => s,n,Answer()
exten => s,n,Wait(1)
exten => s,n,Playback(tt-weasels)
exten => s,n,Hangup()

[incoming_calls]

[internal]
exten => 500,1,Verbose(1|Echo test application)
exten => 500,n,Echo()
exten => 500,n,Hangup()

exten => 1001,1,Verbose(1|Extension 1000)
exten => 1001,n,Dial(IAX2/idefisk,30)
exten => 1001,n,Hangup()

[phones]
include => phones

Do I have to allow or permit that particular WAN IP?
or anything else.

please let me know.
thank you