Why does the coupon field disappear in the WordPress theme on the checkout page?

Question

WordPress

Good afternoon, tell me where to look, when you click on the link "Do you have a coupon? Click here to enter the code,"
the field for entering the code leaves for a second, then it moves back, nothing was picked in the topic, everything costs staff out of the box before the coupon field worked. I can’t figure out where to start looking, I’ll be happy with suggestions or specific instructions, if you need clarification on the settings, I’m ready to say everything that is needed.
Thanks in advance.
APD:
link to the site:
https://www.adv-sound.ru/
to check acc. need to add to cart and try to enter the coupon on the checkout page.

Answer 1

The problem is in the passed parameters of the link attribute.
An attribute is added to the "Click here to enter a coupon" link. data-slimstat-callback="true"
The page uses the SlimStat library , which adds <a>some attributes to the tag. You can see it in the source code of the page on line 597 and on line 594 of its control.
Add the following code to the end of the footer page:

<script type="text/javascript">
jQuery( function( $ ) {
  $('.showcoupon').addClass(' noslimstat'); // Нажмите для авторизации
  $('.showlogin').addClass(' noslimstat'); // Нажмите здесь для введения кода
});
</script>

Should solve the problem. ))