java.security.cert.CertPathValidatorException: Trust anchor for certification path not found IIS server

Question

we are doing a connection with an IIS Server with HttpsUrlConnection in Android Studio project.

These are my statements:

                HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
                connection.setConnectTimeout(15000);
                HashMap<String, String> paramss = new HashMap<String, String>();
                paramss.put("grant_type", "password");
                paramss.put("username", prefer.getString("ws_sq_user",""));
                paramss.put("password", prefer.getString("ws_sq_pwd",""));
                Set set = paramss.entrySet();
                Iterator i = set.iterator();
                StringBuilder postData = new StringBuilder();
                for (Map.Entry<String, String> param : paramss.entrySet()) {
                    if (postData.length() != 0) {
                        postData.append('&');
                    }
                    postData.append(URLEncoder.encode(param.getKey(), "UTF-8"));
                    postData.append('=');
                    postData.append(URLEncoder.encode(String.valueOf(param.getValue()), "UTF-8"));
                }
                byte[] postDataBytes = postData.toString().getBytes("UTF-8");
                connection.setRequestMethod("POST");
                connection.setDoInput(true);

                try {
                    connection.getOutputStream().write(postDataBytes);
                }
                catch (Exception ex)
                {

                }

I receive the error javax.net.ssl.SSLHandshakeException: java.security.cert.CertPathValidatorException: Trust anchor for certification path not found. If I use the same statements with a Ngrok system I didn't have the same problem; on the site there is an SHA256RSA certificate. I downloaded the pfx and cer file but the problem is the same.