Zoom offers a setting to Require media encryption for 3rd Party Endpoints (H323/SIP) that can be set by the host of meetings or at the account level for all members. If this setting is selected, SIP/H.323 devices will be required to use media channel encryption when connecting to the meeting.
There are two options to get connected to this meeting when receiving this message:
Polycom HDX Series (Pages 8-20 & 8-21): Polycom HDX User Manual
LifeSize: SIP Calls / H.323 Calls