ArcGIS Pro 3.4 API Reference Guide
ArcGIS.Desktop.Framework Namespace / Notification Class / Message Property
Example Version

Message Property (Notification)
Gets or sets the message.
Syntax
public string Message {get; set;}
Example
Add a toast notification
Notification notification = new Notification();
notification.Title = FrameworkApplication.Title;
notification.Message = "Notification 1";
notification.ImageSource = System.Windows.Application.Current.Resources["ToastLicensing32"] as ImageSource;

ArcGIS.Desktop.Framework.FrameworkApplication.AddNotification(notification);
Requirements

Target Platforms: Windows 11, Windows 10

ArcGIS Pro version: 3 or higher.
See Also