Create a new account and add details from Extension email sent to you as below:
Label / Account Name / Display Name: Extension Username as per email sent to you
Username / Register Name: Extension Username as per email sent to you
Password: Extension Password as per email sent to you
Sip Server: Extension Sip Server as per email sent to you
Transport Type: TCP
Audio Codec Settings: aLAW
Subscribe for Register: Enabled
Save
Register status should say: Registered
If not, double check the above details or send an email to support.