newbie lab - cannot make snom 821 to manually provision

Phone Type: snom821-SIP
VPN: Off
MAC-Address: 0448C4C31F69 (fake address, just for illustration)

My current Orig and Term provider it's VoIP Innovation.
My VPS Debian 9.4 x64
Fusion PBX v 4.4.3

Extension settings:
Screenshot 2019-04-09 23.15.27.png

Device Provisioning, cannot make the devices to manually provision.

I'm following the instructions on this URL:

My phone setting

Screenshot 2019-04-09 23.04.08.png
this is the setting URL:{mac}

I also try this:

I also try this:

and this:{mac}

running sngrep command: I cannot see any request from the phone
running iptables -L -n command: my IP is not in the REJECTED list, I have my IP whitelisted on the Access Controls

I've another grandstream phone I was able to provision and works fine.

once again, if anyone has a tip I'll be very thankful. :D