How to add a second account and Voicemail to yealink Phone for 3cx

In this video I show you how to add a second user and voicemail box to a yealink phone.
This works with 3cx and all other SIP based phone systems.
You will need to add the voicemail direct dial button (3cx default 999 or 9999), once you access the voicemail via the "Messages" icon in the Yealink Menu.
Or you can add it in the "Advance" tab in the Account settings for Account 2.

[@dovahkween13]

I know this video is 4 years old, but hoping I get a reply here. I am attempting to do exactly this here, and I'm getting register failed. Do I need to add the phone by MAC to the extension in 3CX of the voicemail I'm trying to add to the phone?