PrjMessagesCollection oPrjMessagesCollection = new PrjMessagesCollection(m_oTestProject);
    if (m_oTestProject == null)
{
    ProjectManager oProjManager = new ProjectManager();
    m_oTestProject = oProjManager.CurrentProject;
}
    if (m_oTestProject != null)
{
    Page[] arrPages = m_oTestProject.Pages;
    Function[] arrFunction = arrPages[5].Functions;
    StorableObject oObject1 = arrFunction[0];
    StorableObject oObject2 = arrFunction[1];
    ProjectMessage oProjectMessage = oPrjMessagesCollection.AddMessage(Eplan.EplApi.EServices.IMessage.Region.Externals, 25, "XYZ", oObject1, false, oObject2, "Additional Text");
    Console.WriteLine(" Addded message " + oProjectMessage.GetText() + " to the project");
}