Keeping voice routes to premium phone numbers open makes your Plivo account susceptible to International Revenue Sharing Fraud, also known as Toll-Fraud.
It is advised that you disable outbound calls to premium numbers unless your use-case heavily depends on it.
Mark 'Block Calls To Premium Number' as 'Enabled' and save click 'Save' to update your preference.
Please note that only Admin users can update this setting.
Enabling this feature will block calls to premium numbers across all countries.