Connect Webhooks log success but don't seem to be sent

I am using eSignature API with the C# SDK, working in developer/test mode. I have everything working really well, except for my Connect webhook isn’t getting event notifications. I have a working endpoint which tests well using CURL and a mock SIM payload. And the Admin Connect logs show ‘Success’ for every event. But my callback listener nor the server register any incoming requests. In my code I create a list of Envelope events and later add them to the Envelope object’s EventNotifications list object.

List<EnvelopeEvent> envelopeEvents = new List<EnvelopeEvent> {
    new(){ EnvelopeEventStatusCode = "Sent"},
    new(){ EnvelopeEventStatusCode = "Delivered"},
    new(){ EnvelopeEventStatusCode = "Completed", IncludeDocuments="true"},
    new(){ EnvelopeEventStatusCode = "Declined"}
};

envDef.EventNotifications = new List<EventNotification> {
    new EventNotification("SIM", EnvelopeEvents: envelopeEvents, RecipientEvents: recipientEvents )};

I am able to sign my PDF forms and have the emails sent, and all else seems perfect.

I would have sxpected errors to show in the logs in DocuSign, but all looks well. I might be on the wrong track … anybody see what I might be doing wrong?