The "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" error usually occurs when a Salesforce Administrator attempts to impersonate (Log In As) one of the SightCall Agent Salesforce user account and the Salesforce Administrator account doesn't have Sightcall Agent permission set.
To fix this issue, the Salesforce Administrator's account needs to be given the same access permissions as the SightCall Agent Salesforce user account. This adjustment needs to be done within Salesforce, not SightCall. If that's not possible, then unfortunately, login without using impersonation (Log In As) is the only available option at the time.