I have had the same exact issues and thanks to "kdotten36", I managed to update the Default Zone between the Expressway Core and Edge using the settings recommended above and everything started working now.
I now have IP Phones registering correctly via MRA as well as Cisco Jabber for Windows/iOS, etc.
Configuring Cloud Connected PSTN (CCP) – Easy as 1-2-3!
STEP 1: PREPARE
Before you can configure your CCP in Control Hub, you must procure PSTN services from an authorized Webex Calling CCP Partn...
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This topic is a chance to discuss more about how to read Cisco Unified Communications trace files. In this session, Cisco D...