How do I correctly fill in a webpage form from an android app?

Question

This is the site: https://www.parking-servis.co.rs/eng/edpk
On it, there is the form with a text field and a button. This is the source code from the page:

<div class="edpk-form">
                <form>
                    <input type="hidden" name="_token" value="IvpmhoYWOFx4s5LPLznzg9NY2vnccX0yebxXt2Oi">                    <div class="form-wrap">
                        <div class="input-wrap">
                            <input type="text" name="fine" :class="{'field-error': error}" v-model="vars.plate" :placeholder="lang.enter" required />
                        </div>
                        <div class="submit-wrap">
                            <button class="button blue" type="submit" @click.prevent="findTicket()">{{ lang.search }}</button>
                        </div>
                    </div>
                    <div :id="'pks_eZUuuzPYbGXz6nWn_wrap'" style="display:none;">
                        <input type="text" v-model="vars.pks_MbGfCEQWq6mwwcDm" name="pks_tFMmGu7d5GRyedr1" value="" id="pks_mxhG2rVavA6kdgbG">
                        <input type="text" v-model="vars.eyJpdiI6IjVYZFBwT1VQVXlOcit5Wncvd1E5TXc9PSIsInZhbHVlIjoibGQzbHY0YmJ2bjVCTUFHaDVMb0NyQT09IiwibWFjIjoiYzU5MmYxZjVjZTVkZGE1ZDA4ZmJlZjk2N2ExNGM4MWE2ZWI3ZjA5MjZiNTA0ZGQ3NzdiYzU3MGFkMGU0ZTc5OCJ9" name="pks_valid">
                    </div>
                </form>
            </div>

I'm using this code to fill in the form and press the button, but it doesn't work.

WebView webView = findViewById(R.id.webview_id);
webView.getSettings().setJavaScriptEnabled(true);
        webView.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageFinished(WebView view, String url) {
webView.loadUrl("javascript:(function() { " +
                        "document.getElementsByName('fine')[0].value = 'ABC123XY';" +
"document.forms[0].submit();" +
                        "})()");

It fills the form but the page keeps reloading and nothing happens. I also tried using the code below, the button is pressed correctly, but it looks like the form isn't filled, and the response I get is an error for not filling the form.

webView.loadUrl("javascript:document.querySelector('.input-wrap input[name=\"fine\"]').value = 'ABC1234XY';");
webView.loadUrl("javascript:document.querySelector('.button.blue[type=submit]').click();");

I'm an android developer, but I'm not that skilled in web development, so any help would be appreciated :)