[php] How do I show multiple recaptchas on a single page?

Simple and straightforward:

1) Create your recaptcha fields normally with this:

<div class="g-recaptcha" data-sitekey="YOUR_KEY_HERE"></div>

2) Load the script with this:

<script src="https://www.google.com/recaptcha/api.js?onload=CaptchaCallback&render=explicit" async defer></script>

3) Now call this to iterate over the fields and create the recaptchas:

<script type="text/javascript">
  var CaptchaCallback = function() {
    jQuery('.g-recaptcha').each(function(index, el) {
        grecaptcha.render(el, {
            'sitekey' : jQuery(el).attr('data-sitekey')
            ,'theme' : jQuery(el).attr('data-theme')
            ,'size' : jQuery(el).attr('data-size')
            ,'tabindex' : jQuery(el).attr('data-tabindex')
            ,'callback' : jQuery(el).attr('data-callback')
            ,'expired-callback' : jQuery(el).attr('data-expired-callback')
            ,'error-callback' : jQuery(el).attr('data-error-callback')
        });
    });
  };
</script>