Wordpress Popup doesn't work

Hello,

I installed Wordpress Popup plugin and it does not work. I have this error message:

---
Your active theme:

Has the call to <?php wp_head(); ?> but it is not called directly before </head>

Has the call to <?php wp_footer(); ?> but it is not called directly before </body>
---

I made the required changes, it still does not work.

Could you please help me ?