I've got a Polycom Group 500 series with a Real Touch.
System Sofware Release - 6.1.7-450056
Whenever I try to connect to a Webex Meeting or Skype for Business via SIP or H.323 Extension (E.164) It shows that its connected but then I get a blank screen and no audio.
SIP Registration Server shows as Registration Failed
Registration Server Type is Microsoft
how do you try to connect to an Webex? Via H.323 or SIP? You write your Reg Server is MSFT, so you have an Skype for Business enabled Group? Or how do you use SIP? Might be also a Firewall issue? Do normal H.323 calls work? Detailed info would be nice...
Some stuff about your topic maybe:
Are media ports open on any firewalls between your endpoint and what it is connecting to? Seems like signalling ports are open, but not media ports.