Each internet IP (or each single website visitor) can validate 20 emails per day using your widget. This is a security measure to protect your credits from an abuser. The widget shows a “You performed many validations” error message in this case.
Note that this limit does not mean your widget can validate 20 emails per day. The widget can validate millions of emails per day; the limit is only applied to each user. It means the widget tracks every single website visitor and applies the limit to them separately.