Android Question Problem with Webview Button Click (WebViewExtras)

[Quillok]

hello,
I am currently playing with webviews, but fail to click a button.
It is a simple html and php file, both limited to the most necessary, with an input field and a submit button.
I can write into the field using webviewextras, but the button is not triggered.

can someone possibly tell me why it fails? if i click the button manually, both in the browser and in the webview, the content of the window is normally sent by mail, but i try it programmatically it doesn't work :/

Following the B4A Code, the HTML Code and the PHP Code:

Sub wv_PageFinished (Url As String)
        Dim Javascript As String
        Dim MyWebViewExtras As WebViewExtrasJavascript="document.forms.main.message.value='test1234';document.forms.main.submit();"
        MyWebViewExtras.executeJavascript(wv, Javascript)
End Sub

<!DOCTYPE HTML>
<html>

<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>test</title>
</head>

<body>

    <header class="body">
    </header>

    <section class="body">
    <form id="main" method="post" action="index.php">
 
    <label>Message</label>
    <textarea name="message" placeholder="Type Here"></textarea>
           
    <input id="submit" name="submit" type="submit" value="Submit">
       
</form>
    </section>

    <footer class="body">
    </footer>
</body>
</html>

<?php
    $message = $_POST['message'];
    $from = 'From: test';
    $to = '[email protected]';
    $subject = 'test1234';
   
    $body = "Message:\n $message";
   
   
    if ($_POST['submit']) {
       if (mail ($to, $subject, $body, $from)) {
              echo '<p>sent!</p>';
       } else {
            echo '<p>not sent!</p>';
    }
}
?>