There’s nothing that’s changed between 1.6 and 2.1 in the basic handling of communications between DPMA + Asterisk and the phone. I’d make sure that your license is still valid:
Then I’d look to see if you see SIP MESSAGE traffic from the phone on the Asterisk CLI, and I’d look to see if the response packets are going back to the phone, or not. Perhaps there’s a new router in the middle that’s gobbling SIP MESSAGE traffic with a “smart” ALG capability.
I’d make sure that the Network (https://wiki.asterisk.org/wiki/display/DIGIUM/DPMA+Configuration#DPMAConfiguration-NetworkConfigurationOptions) that you’re applying to the phone profile matches the network segment the phone’s on (just use 0.0.0.0/0 as the cidr for easiest results).
If you’re getting a message requesting a config password and the one you’ve set as the global pin isn’t being accepted, make sure that there are actually phone profiles that have been created:
There a myriad ways for things to go wrong, so the best thing to do is start at the beginning and work forward. Also, if you’re using the Digium Phone Add-on for FreePBX, you’ll want to make sure you’re on the most current version of it and you may want to even compare the generated output of it to what you should be seeing, based on:
https://wiki.asterisk.org/wiki/display/DIGIUM/DPMA+Configuration
Also, if you’re running on a non-standard port, make sure you entered that when you selected “Digium Phone Config Server” from the phone’s Settings boot menu. And, I’d recommend you go ahead and factory default the phone just in case there’s been any attempt to configure it via multiple config methods simultaneously, which can result in unexpected behavior.
Cheers