Hello ASKhalefa,
Thank you for contacting us.
Regarding Auto-Registration: Actually Fortivoice is working in different way and it doesn't have Auto-Registration, it has Auto Provisioning.
Once you configure the Auto Provisioning in FVE and configure your DHCP server with option 66 with the Provisioning link with Https or TFTP, the phones supposed to appear in Fortivoice under Phone System > Devices. And from there, you will see the phones MAC addresses and phones models, then you can select the phone and assign existed extension or create a new one.
For the third party phones, you will need third party license to able to configure them with Auto Provisioning.
For more information Auto Provisioning, please check the below link:
https://docs.fortinet.com/document/fortivoice-enterprise/7.0.1/fortivoice-phone-system-administration-guide/992202/configuring-advanced-phone-system-settings#system_3837743289_2144326
Regarding live debug in CLI, you can use the below:
diagnose debug enable
diagnose debug application <tftpd or cfgfone or other servers> 7
diagnose debug application <tftpd or cfgfone or other servers> display
Those commands will show you the debug of the application but if you want the communication with tftp or other service, it is better to use Traffic capture under Network page or sniffer command as below:
diag sniff packet any "host IP_Address and port PORT_Number" 6 0
Regards
Mohamed Elshehaby
EMEA ETAC