Can't set up Invisible Recaptcha?

Question

reCAPTCHA

Hello, I've already broken my head, I read the instructions on your site, but I just can't set up Invisible Recaptcha. I have a one page website with a callback form. The form submission comes from index1.php
Initially, the form submit button looked like this:

<div class="h1">Оставьте заявку прямо сейчас</div>
                    <div class="form" id="form">
                    <form action="index1.php" method="post">
                        <input type="text" name="name" class="form-text necessality" placeholder="Ваше имя">
                        <input type="text" name="email" class="form-text necessality" placeholder="Ваш email">
                        <input type="text" name="phone" class="form-text necessality" placeholder="Ваш телефон">
                        <button class="form-button">Отправить</button>
                    </form>
                    </div>

I added to the site:

<script src="https://www.google.com/recaptcha/api.js" async defer></script>
<script>
function onSubmit(token) {
  document.getElementById("index1.php").submit();
}
</script>

And changed the button:

<div class="h1">Оставьте заявку прямо сейчас</div>
                    <div class="form" id="form">
                    <form action="index1.php" method="post">
                        <input type="text" name="name" class="form-text necessality" placeholder="Ваше имя">
                        <input type="text" name="email" class="form-text necessality" placeholder="Ваш email">
                        <input type="text" name="phone" class="form-text necessality" placeholder="Ваш телефон">
                        <button class="g-recaptcha" data-sitekey="6LcVlBwUAAAAAC-gI9Ll1D7RD3-AFaapoNB4RVnU" data-callback="OnSubmit">Отправить</button>
                    </form>
                    </div>

What to do next? The Recaptcha logo appeared in the corner. But after clicking the "Send" button, I get a window with the passage of Recaptcha and nothing else. That is, it does not go to the index1.php form.
I read that you need to check the key, how to do it and where to register it ???