Show Error/Warning Message

Hi Team,

Can someone tell me how to show Error/Warning message box?

Here is my code

protected void HMRCAPIConfigDetail_Active_FieldUpdated(PXCache cache, PXFieldUpdatedEventArgs e)
        {

            var row = (HMRCAPIConfigDetail)e.Row;
            var activeAPIConfigs = ActiveAPIConfigs;
            if(activeAPIConfigs != null)
            {
                row.Active = false;
                throw new PXException(Messages.APIActiveErrorMessage);
            }

        }

Thanks