Configuring SIP Registration
You can create SIP user and use this SIP user/password to authenticate your inbound traffic by adding as many SIP User and Password combination in the Ingress Trunk section:
In the "Authoized" dropdown, select "Authorized by SIP Registration."
Then, you will see the table below with one column for SIP Username and one for SIP Password. Thisis where you can create as many SIP user as you need.

Setting up a SIP Interface

The standard SIP Interface only supports IP authorization. To support SIP Registration, you need to create a new SIP Interface.
You can click on "VoIP Gateway" to do that.
After you click on "VoIP Gatway", you can see the standard