How to use OKHTTP to make a post request?

As per the docs, OkHttp version 3 replaced FormEncodingBuilder with FormBody and FormBody.Builder(), so the old examples won’t work anymore.

Form and Multipart bodies are now modeled. We’ve replaced the opaque
FormEncodingBuilder with the more powerful FormBody and
FormBody.Builder combo.

Similarly we’ve upgraded MultipartBuilder into
MultipartBody, MultipartBody.Part, and MultipartBody.Builder.

So if you’re using OkHttp 3.x try the following example:

OkHttpClient client = new OkHttpClient();

RequestBody formBody = new FormBody.Builder()
        .add("message", "Your message")
        .build();
Request request = new Request.Builder()
        .url("https://www.example.com/index.php")
        .post(formBody)
        .build();

try {
    Response response = client.newCall(request).execute();

    // Do something with the response.
} catch (IOException e) {
    e.printStackTrace();
}