External SIP can dial out but not receive connections

I’ve set up my external sip as follows:

http://www.freepbx.org/support/documentation/howtos/howto-setup-a-remote-sip-extension

I can make calls from the extension but when I try and dial the extension I can’t get through. The error message that a softphone extension returns is “Server can not be reached”

Could it be a port forwarding issue?

The documentation says

“UDP/10001-20000 -> Forward to 192.168.1.100”

My router allows me to forward a range to a single port else I need to do each one, one at a time.

So initially I forwards 10001-20000 to 10001

It would take an age to enter each port individually.

Device options are as follow; I think there is possibly an issue here.

secret: *****
dtmfmode: rfc2833
canreinvite: no
context: from-internal
host: dynamic
type: friend
nat: yes
port: 5060
qualify: yes
callgroup
pickupgroup
disallow
allow
dial: SIP/210
accountcode
mailbox: [email protected]
vmexten
deny
permit

I am guessing that the context is wrong but I dotryn’t know what else I might

On further investigation besides no receiving calls from external phone numbers or ring groups,this extension can only dial other extensions, not actual phone numbers.