If the Salesforce Service Cloud Voice Agent receives the following exception, then the Agent doesn’t have “Contact Center Connected App” permission set.

Exception:

“Insufficient Privileges
You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary. For more information, see Insufficient Privileges Errors.”

In the browser Network tab, the error will be “500 Server Error”.

Once the “Contact Center Connected App” permission set is assigned to the Agent, the issue will be resolved.