SSLHandshakeException - Chain chain validation failed, how to solve?

in my application I am trying to do a HTTPS POST request to my server.However, I keep getting SSLHandshakeException - Chain chain validation failed, all the time. I tried to send a request using POSTMAN and I got a response from the server. What can be causing this error when I try to send the request from the application?

Here a code snippet where I try to send the post request:

   public static JSONObject getDataLibConfiguration(Context context) throws HttpRequestException {    int statusCode = 0;    JSONObject commonInformation;    HttpsURLConnection connection = null;    try {        commonInformation = ConfigurationProcessor.getCommonInformation(context);        if (commonInformation == null) {            return null;        }        URL url = new URL(BuildConfig.SERVER_CONFIG_URL);        if (BuildConfig.DEBUG) {            LogUtils.d(TAG, "url = "+ url.getPath());        }        connection = getHttpsConnection(url);        connection.setDoOutput(true);        connection.setDoInput(true);        connection.setRequestMethod("POST");        connection.setRequestProperty("Content-Type", "application/json; charset=UTF-8");        connection.setRequestProperty("Content-Encoding", "gzip");        byte[] gzipped = HttpUtils.gzip(commonInformation.toString());        cos = new CountingOutputStream(connection.getOutputStream()); //<-- This is where I get the exception        cos.write(gzipped);        cos.flush();        statusCode = connection.getResponseCode();        // More code her }private static HttpsURLConnection getHttpsConnection(URL url) throws IOException, GeneralSecurityException {        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();        try {            SSLContext sslContext = SSLContext.getInstance("TLS");            MatchDomainTrustManager myTrustManager = new MatchDomainTrustManager(url.getHost());            TrustManager[] tms = new TrustManager[]{myTrustManager};            sslContext.init(null, tms, null);            SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();            connection.setSSLSocketFactory(sslSocketFactory);        } catch (AssertionError ex) {            if (BuildConfig.DEBUG) {                LogFileUtils.e(TAG, "Exception in getHttpsConnection: "+ ex.getMessage());            }            LogUtils.e(TAG, "Exception: "+ ex.toString());        }        return connection;    }