Recurrence Google calendar event not working

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C#

Google

calendar

I have try following code but not success. giving error.

What I have tried:

Event newEvent = new Event
{
Summary = item.CalendarString,
Location = "",
Description = "",

Start = new EventDateTime()
{
DateTime = DateTime.Parse(startDate.ToString("yyyy-MM-dd ") + startTime),//DateTime.Parse("2018-05-28T09:00:00-07:00"),
TimeZone = timeZone,
},
End = new EventDateTime()
{
DateTime = DateTime.Parse(startDate.ToString("yyyy-MM-dd ") + endTime),// DateTime.Parse("2018-05-28T10:00:00-07:00"),
TimeZone = timeZone,
},
Recurrence = new String[] { "RRULE:FREQ=WEEKLY;UNTIL=" + enddateRecurrence + ";BYDAY=" + dayss },

};