webView white screen

public class MainActivity extends AppCompatActivity {

    private WebView webView;
    private TextView txt_address;
    private Handler handler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        txt_address = findViewById(R.id.txt_address);

        // WebView Initialization
        init_webView();

        // JavaScript event response via handler
        handler = new Handler();
    }

    public void init_webView() {

        // WebView Settings
        webView = (WebView) findViewById(R.id.webView_address);

        webView.setWebViewClient(new WebViewClient() {

            @Override
            public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
                handler.proceed();
            }
        });

        webView.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);

        webView.setWebViewClient(new SslWebViewConnect());
        // Allow JavaScript
        webView.getSettings().setJavaScriptEnabled(true);

        // Allow window.open in JavaScript
        webView.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);

        // Assign a class that defines a function to correspond to JavaScript events
        webView.addJavascriptInterface(new AndroidBridge(), "TestApp");

        // Set web client to Chrome
        webView.setWebChromeClient(new WebChromeClient());

        webView.getSettings().setDomStorageEnabled(true);

    }

    // webview url load.php file address
    // // webView.loadUrl("http://naver.com");
    // This is the bottom
    // I put the php address.

    private class AndroidBridge {
        @JavascriptInterface
        public void setAddress(final String arg1) {
            handler.post(new Runnable() {
                @Override
                public void run() {
                    txt_address.setText(String.format(arg1));

                    // Cannot be reused without initializing WebView
                    init_webView();
                }
            });
        }
    }

    public class SslWebViewConnect extends WebViewClient {

        @Override
        public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
            handler.process(); // proceed even if SSL error occurs!
        }

        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;// application handles url directly
        }
    }
}

<?php
header("Content-Type: text/html; charset=UTF-8");
?>

<script src="https://t1.daumcdn.net/mapjsapi/bundle/postcode/prod/postcode.v2.js"></script>
<script>
new daum.Postcode({
    oncomplete: function(data) {
        if(data.userSelectedType=="R"){
            // userSelectedType : The type of address selected by the user in the search results
            // // return type : R - roadAddress, J : jibunAddress
            // TestApp is the name registered on Android
            window.TestApp.setAddress(data.roadAddress);
        }
        else{
            window.TestApp.setAddress(data.jibunAddress);
        }        
    }
}).open();
</script>