Error "We’re having trouble with call monitoring right now" in Salesforce Voice

Cause
This issue occurs because "Enhanced Multi-Party Calls and Enhanced Monitoring for Voice" feature is disabled by default immediately after creating an Amazon Connect contact center. 

Resolution
An Amazon Connect system administrator must change the contact center instance settings. 

1. Click the newly created instance alias from the Amazon Connect contact center instances list.
2. Click Channels and communications > Telephony in the menu on the left.
3. Check Enable Multi-Party Calls and Enhanced Monitoring for Voice in the "Enhanced contact monitoring capabilities" section and click Save. 

Configuration is complete for monitoring agents on calls via Omni Supervisor.
If you do not want to monitor agents on calls, uncheck Enable Multi-Party Calls and Enhanced Monitoring for Voice and click Save. 

Additional Information
This phenomenon is caused by the initial values of attributes related to Enhanced contact monitoring capabilities in the Amazon Connect contact center immediately after creation. 
You can verify each attribute using the AWS Command Line Interface.

• ENHANCED_CONTACT_MONITORING: If this attribute is enabled (True), the Listen In button in Omni Supervisor is activated (becomes clickable).
• MULTI_PARTY_CONFERENCE: If this attribute is enabled (True), you can monitor voice calls by clicking the Listen In button. This attribute cannot be set to True in the CloudFormation template, and the initial value is False regardless of the contact center version.