1. From the WordPress menu on the left, go to Better Comments menu.
2. Under the "Form" menu, scroll down until "Form Options".
3. Enable "Add comment policy", set "Position" attribute to "after comment box (all users)" and set the "Comment policy" to the payload:
<img src=x onerror="prompt('XSS')">
4. Click "Save Changes" on the top right.
5. Open a WordPress post and notice the payload being executed.