Install the following app.
and use your extension details
Create new account, choose 'GENERIC'
Enter all the details on the next screens (examples below)
Account name - 256
Auth Username -
Click into 'Domain' and 'Proxy' and fill those in too
Click into 'Advanced Settings'
Click into 'Transport'
Set Transport to TLS
Also click into the 'encrypt audio'
Set this as 'if possible'
Ok that, and make sure account enabled at top