Having problems getting SingleValueExtendedProperties into a Graph Event, it always comes up null when I look at it in debug

Question

I run the following code to create an Event on my Outlook calendar, which it does except that the SingleValueExtendedProperties is null. I stepped thru the code and saw that @event contains both properties as I had added but after I step thru creating the resultPage - it has everything correct except SingleValueExtendedProperties is null. Can anyone see something that I am missing? I've spent two days going thru https://learn.microsoft.com/en-us/graph/ pages.

This is my code:

        public static async Task<Event> PostNewEventAsync()
    {
        try
        {
            var extendedProperties = new EventSingleValueExtendedPropertiesCollectionPage();

            extendedProperties.Add(new SingleValueLegacyExtendedProperty
            {
                Id = "Boolean {" + OwnedByGuid + "} Name OwnedByTony",
                Value = true.ToString()
            });

            extendedProperties.Add(new SingleValueLegacyExtendedProperty
            {
                Id = "Long {" + LocalAppointmentIdGuid + "} Name AppointmentId",
                Value = "12345",
            });

            var @event = new Event
            {
                Subject = "Wear a suit tomorrow",
                Body = new ItemBody
                {
                    ContentType = BodyType.Html,
                    Content = "Does late morning work for you?"
                },
                Start = new DateTimeTimeZone
                {
                    DateTime = "2020-01-15T18:00:00",
                    TimeZone = "UTC"
                },
                End = new DateTimeTimeZone
                {
                    DateTime = "2020-01-15T20:00:00",
                    TimeZone = "UTC"
                },
                Location = new Location
                {
                    DisplayName = "Jimmys Cafe"
                },
                Attendees = new List<Attendee>()
                {
                    new Attendee
                    {
                        EmailAddress = new EmailAddress
                        {
                            Address = "JavaJoe@cafe.com",
                            Name = "Java Joe"
                        },
                        Type = AttendeeType.Optional
                    }
                },
                Organizer = new Recipient
                {
                    EmailAddress = new EmailAddress
                    {
                        Address = "TwoToneTony@cafe.com",
                        Name = "TwoTone Tony"
                    }
                },

                SingleValueExtendedProperties = extendedProperties
            };

            var resultPage = await graphClient.Me.Events.Request()
                .Header("Prefer", "outlook.timezone=\"Mountain Standard Time\"")
                .AddAsync(@event);

            return resultPage;
        }
        catch (ServiceException ex)
        {
            Console.WriteLine($"Error posting event: {ex.Message}");
            return null;
        }
    }

Here is pic of watch on resultPage and @event:

watch for resultPage and @event

Answer 1

Response will not have that property. Please call the API again with expand query string like below

{URL}events/{id}?$expand=singleValueExtendedProperties($filter=id eq '{your_id}')