Back in the Sipura Ext. 1 section, set the following details:
General:
Line Enable: yes
SIP Settings:
SIP Port: 5060
Proxy and Registration:
Proxy: [Axon SIP Server Name]
Register: yes
Register Expires: 600
Subscriber Information:
Display Name: [whatever you like]
User ID: [Axon SIP User ID for the extension]
Password: [Axon SIP Password for the extension]
Audio Configuration:
Preferred Codec: G711u
Use Pref Codec Only: no
Silence Supp Enable: no
DTMF Tx Method: Auto
Leave all other settings as they are. Click "Submit all changes".