Null value when Pass values [FromBody] to post method by Postman plugin

You can't bind a single primitive string using json and FromBody, json will transmit an object and the controller will expect an complex object (model) in turn. If you want to only send a single string then use url encoding.

On your header set

Content-Type: application/x-www-form-urlencoded

The body of the POST request message body should be =saeed (based on your test value) and nothing else. For unknown/variable strings you have to URL encode the value so that way you do not accidentally escape with an input character.

Alternate 1

Create a model and use that instead.

Message body value: {"name":"saeee"}

c#

public class CustomModel {
    public string Name {get;set;}
}

Controller Method

public HttpResponseMessage Post([FromBody]CustomModel model)

Alternate 2

Pass primitive strings to your post using the URI instead of the message body.