ASP.NET web api cannot get application/x-www-form-urlencoded HTTP POST

Quoting from here:

By default, Web API tries to get simple types from the request URI. The FromBody attribute tells Web API to read the value from the request body.

Web API reads the response body at most once, so only one parameter of an action can come from the request body. If you need to get multiple values from the request body, define a complex type.

Second, the client needs to send the value with the following format:

=value

Specifically, the name portion of the name/value pair must be empty for a simple type.

So, if you want to post data in the format data=string, you have to create complex type.

public class MyFormData
{
    public string Data { get; set; }
}

And update your controller like so:

public void Post(MyFormData formData)
{
    //your JSON string will be in formData.Data
}

Of course, other alternatives for you is to change the content type to JSON, but really depends on your requirements.

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