Workflow Event Handler Not Firing.

I’ve been having trouble getting a custom event handler to fire. I’ve followed this process...

• Workflow Api - Adding additional Status & Changing workflow to Shipment Screen from Code

...as closely as I could, and while the action that fires the event runs, the transition triggered by the event does not. 

I feel like I’m missing something obvious, but I just can't put my finger on it. 

I’m working with 24R1 Build 24.101.0059.

For context, this is more an exercise in personal edification than looking for a workaround. 

Any input would be appreciated. 

 // Acuminator disable once PX1016 ExtensionDoesNotDeclareIsActiveMethod extension should be constantly active
 public class APInvoiceExtZ : PXCacheExtension<PX.Objects.AP.APInvoice>
 {
     public class Events : PXEntityEvent<APInvoice>.Container<Events>
     {
         public PXEntityEvent<APInvoice> DescChanged;
     }
 }



 // Acuminator disable once PX1016 ExtensionDoesNotDeclareIsActiveMethod extension should be constantly active
 public class APInvoiceEntry_Ext : PXGraphExtension<APInvoiceEntry>
 {

     public PXAction<APInvoice> ChangeDescription;
     [PXUIField(DisplayName = "ChangeDescription")]
     [PXButton]
     protected virtual IEnumerable changeDescription(PXAdapter adapter)
     {
         Base.Document.Current.DocDesc = "The Action changed this Description";

         APInvoiceExtZ.Events
             .Select(e => e.DescChanged)
             .FireOn(Base, Base.Document.Current);

         return adapter.Get();

     }


     #region Entity Event Handlers
     public PXWorkflowEventHandler<APInvoice> OnDescChanged;
     #endregion
 }



 // Acuminator disable once PX1016 ExtensionDoesNotDeclareIsActiveMethod extension should be constantly active
 public class APInvoiceEntry_WorklowExt : PXGraphExtension<APInvoiceEntry_Workflow, APInvoiceEntry_Ext, APInvoiceEntry>
 {
     public sealed override void Configure(PXScreenConfiguration config) { Configure(config.GetScreenConfigurationContext<APInvoiceEntry, APInvoice>()); }

     protected static void Configure(WorkflowContext<APInvoiceEntry, APInvoice> context)
     {
         context.UpdateScreenConfigurationFor(screen =>
         {
             return
             screen
             .WithActions(actions =>
             {
                     actions.Add<APInvoiceEntry_Ext>(g => g.ChangeDescription, a => a.WithCategory(PredefinedCategory.Actions));
             })

             .WithHandlers(handlers =>
             {
                     handlers
                     .Add(handler =>
                     {
                         return
                         handler
                         .WithTargetOf<APInvoice>()
                         .OfEntityEvent<APInvoiceExtZ.Events>(e => e.DescChanged)
                         .Is<APInvoiceEntry_Ext>(g => g.OnDescChanged)
                         .UsesTargetAsPrimaryEntity()
                         .DisplayName("OnDescChanged");
                     });

             })

             .UpdateDefaultFlow(flow =>
                     flow
                     .WithFlowStates(fss =>
                     {
                         fss.Update<APDocStatus.hold>(flowState =>
                         {
                             return flowState
                             .WithActions(actions => actions.Add<APInvoiceEntry_Ext>(g => g.ChangeDescription))
                             .WithEventHandlers(handlers => { handlers.Add<APInvoiceEntry_Ext>(g => g.OnDescChanged); });
                         });

                     })

                     .WithTransitions(transitions =>
                     {
                         transitions.UpdateGroupFrom<APDocStatus.hold>(ts =>
                             ts.Add(t => t
                                 .To<APDocStatus.balanced>()
                                 .IsTriggeredOn<APInvoiceEntry_Ext>(g => g.OnDescChanged)
                             )
                         );
                     })
             );
         });
     }
 }