First, you must provision the phone device in the Admin Portal by going to Configuration > Provisioning > Phones.
Once you've added the phone along with its MAC address, you will then see an Autprovisioning URL. This is the URL you will put into the phone that will provide the settings for the phone from the server.
For Polycom devices -
On the Polycom Phone press the Menu Button
Scroll to the Status… menu item and press Select
Scroll to the Platform… menu item and press Select
Scroll to the Phone… menu item and press Select
Scroll down see your phone IP address on the screen similar to IP: XXX.XXX.XXX.XXX
Enter that IP address in your web browser to access the phone's admin interface.
Open the Web Interface of the Polycom device and “Login As Admin” (default password is 456).
Navigate to “Settings” -> “Provisioning Server.”
Set “Server Type” to HTTPS.
In “Server Address” enter the provisioning URL from the VoIP Portal (shown above)
Clear the fields of “Server User” and “Server Password.”
Press “Save” in the bottom of the page and confirm the changes.
For Grandstream devices -
Press the up arrow on your phone to get the phone's IP address.
Enter the IP address into a web browser, and login with the default username and password: admin / admin
Then, go to Maintenance > Upgrade & Provisioning and enter the Autoprovisioning URL into the Config Server Path box and be sure to select HTTPS under Upgrade via. Do NOT include https:// in the URL for the Config Server Path.
Then, click the Provision link in the top right or simply reboot the phone. The phone will contact the server to download the settings such as the extension that should be on the phone. It may take several reboots before the first provisioning is successful.