the nch guide needs an update, we're addressing that currently.
your guide is quite good, however your methodology is not the way we intended - while it does work of course, our idea is just a little simpler and is summarised like so: (this is very brief)
- create an external line in axon with a nominated username/password and blank server field, set it to ring on a nominated group
- enter those username/password details into the sipura's PSTN section User ID and Password fields
- set the FXO dialing plan to forward to the line you configured in axon - [username]@[axon ip address]
- save the changes in the FXO and then wait for the FXO to register with Axon (you will see the log message 'External Line [name] is at : [ip address]:[port])
- in axon edit your dialing plan and create a new dial rule and set it to use axon's sipura line
- edit any relevant extensions and set them to use the sipura dial rule
we deliberately want the sipura device to register with axon, that is definitely not a mistake in our guide, the whole 'let the other device register with axon' design was very carefully thought out and its quite useful once you understand how it works.
using this method you also won't see any 'Register attempt failed' log messages ever.
this is how i configured my own sipura box at home and it works great for me.