C# Facebook DateTime

I am creating FB event from C# code, and I need to populate start_time field. which is of the below format.

From FB:
Precise-time (e.g., '2012-07-04T19:00:00-0700'): events that start at a particular point in time, in a specific offset from UTC. This is the way new Facebook events keep track of time, and allows users to view events in different timezones.


I have tried all other site, which says ToString("s"), ToString("o"), ToUniveralTime(), CultureInfo("en-US") and nothing worked. But If i copy paste the exact '2012-07-04T19:00:00-0700' in date field, it worked.
I am thinking something like this ToString("yyyy-MM-ddTHH:mm:ss-xxxx")
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