Has the phone been provisioned before?

If the phone has been provisioned on the platform before and you are reprovisioning after a factory reset, you must delete it from the inventory and then add it back in; otherwise, the provision will fail.

Ensure the phone has an internet connection/IP address.

It's also important to double-check that the phone is getting an IP address from the DHCP server; it's very easy to miss this and spend hours troubleshooting when the issue was simple.

Disable SIP ALG on the router.

Enabling SIP ALG will almost always cause problems, and disabling it should be your top priority if you're having issues with the phones in general.

Double-check the MAC address.

Putting in the wrong MAC address tends to account for most provisioning errors. It's easy to forget to check this, but if your phone isn't provisioning, it's a good habit always to double-check the MAC you've used. Check the MAC written on the physical device, NOT on the box, just in case the device was shipped in a different box.

If you navigate to "Inventory>Phone Hardware," you should see a list of all your devices with the MAC Address. A green check indicates that the phone is connecting to us.

If you are certain that everything else is configured correctly, this may be a firewall or DNS issue (see below). 

Check the line configuration.

Head into the Inventory tab and make sure the line is configured correctly. Sometimes, specific actions can cause the line to become malformed. If you're unsure, just remove and re-add it. The phone will not be provisioned if no line is provided.

Change the protocol.

If you have tried provisioning via HTTPS, then try HTTP instead, and vice versa.

Remove the device, then add it back again.

Deleting the device from the inventory and then adding it back in again will ensure that the settings or the config file are intact.

Factory reset the device.

Sometimes, the device can have some settings from a prior setup that cause issues. Making sure you factory reset the device before provisioning can help avoid these issues.

Update the firmware.

Out-of-date firmware on a device is a notorious cause of provisioning faults, especially on older devices. Before provisioning, make sure that the phone has the latest firmware.

Check the device on a separate network.

This won't fix the issue, but it will rule out the platform as a problem. Check to see if you can provision a phone on a network separate from the main one. It will be most useful if this is a network that KNOWS has working phones on our platform. If you do this and the phones provision fine, you now know the issue is on the local network.

Check the firewall settings.

Make sure nothing in the firewall is blocking SIP traffic. Check here for information on preparing your network for phones.

Change the DNS settings.

Faulty DNS can cause various problems, including phone system issues. Try changing the DNS on the phone to the following:

Primary DNS: 1.1.1.1

Secondary DNS:  8.8.8.8

Put the phone on a static IP address.

Occasionally, a device may receive erroneous information from the DHCP server. Sometimes, it's worth moving the device onto a static IP to prevent this from potentially being an issue.