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DateTime.ParseExact Failing to convert to correct date

I am using FullCalendar. Now there is a code where I get a Date/Time from FullCalendar API. This is called startDate and has a below format:
String. An ISO8601 string representation of the start date. It will
have a timezone offset similar to the calendar’s timeZone e.g.
2018-09-01T12:30:00-05:00. If selecting all-day cells, it won’t have a
time nor timezone part e.g. 2018-09-01.
Let us for this question, assume that startStr is 2020-11-15T23:00:00-08:00
I have an ASP.NET MVC backend, where I send this string using Javascript.
The server receives the correct string as above i.e. 2020-11-15T23:00:00-08:00
Now, there is a code where I parse this date to the DateTime object
DateTime sdt = DateTime.ParseExact(sstartStr, "yyyy'-'MM'-'dd'T'HH':'mm':'sszzz", CultureInfo.InvariantCulture)
But here, this date/time is parsed as 11/16/2020 12:30:00 PM.
(You can try parsing the said date using the above code, the output will be wrong as above.)
Am I missing something ?

How to strip timezone from DateTime in .NET Core

I have a use case that I'm not sure how to solve in a nice way.
I'm currently developing a .Net Core WebApi that is receiving data from various current systems, from a cross the whole world. Which I then process and lastly I commit it to SAP through oData endpoint.
The problem I'm having is on of parameters I'm receiving in the body payload, is a DateTime. Previous I have not have any issues. But not long ago I started getting data from a other system which deliverers it in a slightly differently way.
Previously this was the format I got: 2020-09-16T16:30:00 not problem with it. But the new system looks like this: 2020-09-16T16:00:00 -05:00 Could also end in +08:00.
The problem I'm facing is that SAP needs to get in local time. But in the my code it converts this: 2020-09-16T16:00:00 -05:00 to 2020-09-16T23:00:00 when I see the incoming payload in the controller.
I have searched quite a bit to find a solution. But 99% only suggest using UTC time, which is not a option for me.
Another option is to use DateTimeOffset, which I have tried but can't the time conversion to use localTime.
My question is. Are it not possible to custom convert to strip the timezone before it hits the controller?

Generarally when you're working with datetime data that includes offsets for time zone the DateTimeOffset type is a good place to start. The sample string 2020-09-16T16:00:00 -05:00 can be passed to DateTimeOffset.Parse() to get a correct DTO value with timezone information attached. From there you can get the local time, UTC time or a DateTime value with the timezone stripped.
string source = "2020-09-16T16:00:00 -05:00";
string fmt = #"yyyy-MM-dd\THH:mm:ss zzz"
// Same as input
Console.WriteLine(DateTimeOffset.Parse(source).ToString(fmt));
// Adjusted to your local timezone
Console.WriteLine(DateTimeOffset.Parse(source).ToLocalTime().ToString(fmt));
// DateTime portion of the source, timezone offset ignored
Console.WriteLine(DateTimeOffset.Parse(source).DateTime.ToString());
Getting the UTC time is simple too via the UtcDateTime property.
It sounds like what you want is the last one - just the date and time from the inputt string with the timezone offset stripped. If you just want the corresponding local time then DateTime.Parse should give that to you directly.
The JsonSerializer class doesn't support this format for DateTimeOffset so you might have some trouble getting it converted before hitting your controller. In that case you'd need to accept a string and do the conversion by hand in your code. You also might need to investigate the TryParseExact method.

Use DateTime.Parse() , for example
string timeInString1 = "2020-09-16T16:00:00 -05:00";
DateTime moment1 = DateTime.Parse(timeInString1);
string timeInString2 = "2020-09-16T16:00:00 +08:00";
DateTime moment2 = DateTime.Parse(timeInString2);
string timeInString3 = "2020-09-16T16:30:00";
DateTime moment3 = DateTime.Parse(timeInString3);
but momen1, momen2, or moment3 is non-timezone awareness value.

Setting a dateTime with only two characters as milliseconds

I have a WCF webservice I use to set some date using the following code :
foo.StartDateTime = DateTime.UtcNow;
Unfortunately, at the output of the WCF webservice, the date is the following :
<a:startDateTime>2019-01-30T08:54:13.698Z</a:startDateTime>
The issue is that the millisecond part must be on 2 characters only because our middleware can process only date like that. I know it's valid ISO 8601 but still.
How is it possible to set the date that will be in the response of the WS with only two characters ?

C# DateTimeInvalidLocalFormat - How to set timezone to UTC

I'm working in a EasyPost integration making a class library to make the use of their API simpler and I'm getting this error:
Managed Debugging Assistant 'DateTimeInvalidLocalFormat' has detected a problem in 'C:\Projects\TestClient.vshost.exe'.
Additional information: A UTC DateTime is being converted to text in a format that is only correct for local times. This can happen when calling DateTime.ToString using the 'z' format specifier, which will include a local time zone offset in the output. In that case, either use the 'Z' format specifier, which designates a UTC time, or use the 'o' format string, which is the recommended way to persist a DateTime in text. This can also occur when passing a DateTime to be serialized by XmlConvert or DataSet. If using XmlConvert.ToString, pass in XmlDateTimeSerializationMode.RoundtripKind to serialize correctly. If using DataSet, set the DateTimeMode on the DataColumn object to DataSetDateTime.Utc.
I get this error when I call the Create method in the EasyPost Shipment object. Code below:
Shipment shipment = new Shipment() {
to_address = toAddress,
from_address = fromAddress,
parcel = parcel
};
shipment.Create();
This create function probably makes a call to their REST API and is trying to convert a json response into one of their models.
To solve the error I'm trying to set the UTC as the default of my library so whenever I use DateTime.ToString() I use the DateTime.ToString("o"). I don't know if this would actually solve the problem, but I don't know how to force it (use UTC as the library default). I have tried the piece of code below, but it doesn't work
CultureInfo newCulture = CultureInfo.InvariantCulture;
Thread.CurrentThread.CurrentCulture = newCulture;
Can you help me?

I'm one of the developers on the EasyPost client libraries.
As far as I can find in some basic research, there's no (easy) way to set a default time zone for a C# application. Most of the blog posts and other SO answers I found suggest using utility functions to convert a UTC datetime object to a local datetime object when trying to display it to a string.
EasyPost's API returns all datetimes in UTC time + timezone information (ex. 2022-10-24T12:37:24-06:00), which is accounted for when the JSON is deserialized into a DateTime object in the C# client library.

JSON parse DateTime

From the server I get this string
[{\"id\":\"9b77ff1e-350e-44d8-8860-15e80f4d8a22\",\"code\":\"C\",\"name\":\"0%\",\"validFrom\":\"2013-07-01T00:00:00Z\",\"validTill\":null,\"active\":1,\"vatProc\":0.0,\"createdAt\":\"2015-02-01T13:04:17.733Z\",\"updatedAt\":\"2015-02-01T13:04:17.733Z\"}]
On the client side I then convert it to a json object using JSON.parse which produces the result:
[
{
active:1
code:"C"
createdAt:"2015-02-01T13:04:17.733Z"
id:"9b77ff1e-350e-44d8-8860-15e80f4d8a22"
name:"0%"
updatedAt:"2015-02-01T13:04:17.733Z"
validFrom:"2013-07-01T00:00:00Z"
validTill:null
vatProc:0
}
]
Which is as you would expect if it where not for the date fields.
The dates are on server translated to UTC.
I know I can pass a function to parse the function to do the conversion.
I would just like to format the date's so that the regular parse would do it "right" if you know what I mean
I saw on the net that there is no "right" way and that every case what I was reading about on the net is working with conversion on the client side.
So is there really no way to tell the regular json parser that that is a date?
I have the option to convert that date-time to what ever would work on the server
ClientSide: AngularJS
ServerSide: C# WCF / json
EDIT:
The problem that I am having is that if I use for instance the ValidFrom as a model in AngularJS it is complaining that it is not a date witch it really is not
AngularJS error:
Expected `2013-07-01T00:00:00Z` to be a date

Before I send a date to the client I set the DateTimeKind property to utc
SomeObject.Date= DateTime.SpecifyKind(SomeObject.Date, DateTimeKind.Utc);
Before saving any date to the server I do:
SomeObject.Date= SomeObject.Date.ToUniversalTime();
The only requirement on the client is to use momentjs format() method in order to convert the date to ISO-8601
Following this method JSON always handles times correctly on the client (at least it has worked fine so far for me)
This helped me a lot