Solved Yealink phone won't register - 3CX is returning 403 Forbidden when phone attempts to download anything from 3CX

[kaiserh]

I have a Yealink SIP-T48U that was previously working as an extension in 3CX.
The user who's extension it was was synced from Office 365.
After the user left, I went into the Office 365 config and stopped that user syncing.
Settings > Microsoft 365 > User Sync > select user and hit Delete.
I did not remove the phone from the user first.

I have since factory reset the phone multiple times, and it will not provision from 3CX.

I have manually added it (via the MAC address) as an extension for another user, and got the provisioning URL. I logged into the web interface of the phone and entered the URL, and told the phone to auto provision.

When I do a packet capture in 3CX while this is happening, I can see the HTTP GET requests from the phone, and 3CX is replying to all of them HTTP/1.1 403 Forbidden

The phone tries to fetch a number of different URLs, and received a 403 Forbidden on all of them.
e.g.:
http://172.16.16.40:2000/provisioning/random-characters/mac-address.boot
http://172.16.16.40:2000/provisioning/random-characters/y000000000000.boot
http://172.16.16.40:2000/provisioning/random-characters/y000000000109.cfg
http://172.16.16.40:2000/provisioning/random-characters/mac-address.cfg

On my computer, using curl, I can fetch the last URL with the phone's MAC address .cfg and it returns a text file with the phone configuration. When the phone fetches it however it's given a 403 from nginx.

I downloaded the .cfg file through my web browser and then uploaded that to the phone via the phone's web interface, it took the config and rebooted. When it came up however although it has, e.g., the 3CX PBook icon at the bottom of the screen, it says No Service at the top of the screen and the phone is not visible in the Phones list in 3CX.

After this, I've done another packet capture while the phone was booting up and provisioning but it's still getting 403 Forbidden, even on things like the phonebook - e.g.

http://172.16.16.40:2000/provisioning/random-characters/yealink_phonebook.xml - 403 Forbidden

Is there somewhere where the MAC address or even IP address of the phone might be blacklisted in the PBX?

 

[kaiserh]

OK, I've solved this.
Security > IP Blacklist > Remove phone's IP address from the blacklist.
What I'm guessing happened was the phone kept trying to register however the user and extension it was registering as had been deleted, so it was blacklisted.