ESP8266 cannot read POST parameters

I'm working on a simple REST server. I made method to handle http://<esp8266_IP>/test. The GET method works like a charm and I got the response. Then I tried to send a POST with a JSON data (I used PostMan) but I cannot read anything.

Searching online I read ESP8266 library cannot parse JSON and in that case I can found plain text into server.arg("plain"). I tried that but no success

How can I read the data into the POST method?

ESP8266WebServer server(80);
...

void handleTest()
{
    if (server.method() == HTTP_GET)
    {
        ...
    }
    else if (server.method() == HTTP_POST)
    {
        String message = "POST\nHeaders:\n";
        for (uint8_t i = 0; i < server.headers(); i++)
        {
            message += server.headerName(i) + ": " + server.header(i) + "\n";
        }
        message += "\nRequest params:\n";
        for (uint8_t i = 0; i < server.args(); i++){
            message += " " + server.argName(i) + ": " + server.arg(i) + "\n";
        }
        server.send(202, "text/plain", message);
    }  
}
...
void setup()
{
    WiFi.begin(ssid, password);
    Serial.println("");

    // Wait for connection
    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
    }

    if (MDNS.begin("esp8266")) {
        Serial.println(F("[Server] MDNS responder started"));
    }

    server.on("/test", handleTest);
}