Why does recaptcha return ""?

Question

JavaScript

Hello, I have
a code

<script src="https://www.google.com/recaptcha/api.js" async defer></script>
<div class="g-recaptcha" data-sitekey="**************************"></div>

When I fill in the captcha, I call the grecaptcha.getResponse() method;
And in response I get "", why is this happening?