Polycom VoIP card on SoundStructure or phone is not able to register to Avaya PBX using SIP protocol. Other non-polycom phones working fine with Avaya server.
Network setup was correct, the non-polycom phones were working proplerly from within the same network. To double check credentials, I helped them remotely & requested they test the credentials using a Softphone app like Zoiper, the same credentials did not work on the Softphone which made me believe the issue was not on the Polycom product. I also used this URL to help customer realize that the phone was not registered to the SIP server.
Taking a closer look - The phone was configured to use SIP protocol. The non-polycom phones, though they were using same Avaya server and it seemed like they did have proper network setup on VLANs, once I asked to remotely look at the non-polycom configuration I noticed these other phones were setup for H.323 & not SIP.