It does not work

Second this… I am just trying this plugin for the first time, and it doesn’t seem to do anything in WordPress 5.8.1. I’ve tried twice to remove a category from a set of posts: bulk edit, click the “Remove from category” checkbox, then the category in the list above that I want to remove the posts from, and click Update. No change. All of the posts are still in the category I want to remove them from.

Update: After reading another thread that mentioned this uses AJAX, I decided to have the JavaScript Console open while I was trying to run this. I got the following error message:

XMLHttpRequest cannot load https://…/admin-ajax.php due to access control checks.

I’m an experienced developer, but AJAX is one of my weak spots, so I’m not sure exactly what’s going on here, but I’m going to try to dig into it a bit more.

Ah-ha! Success! I found a StackExchange thread that offered a solution. I tested it (with a tweak to make it pull the site’s URL dynamically) and added this code into the plugin directly, and it solved the problem for me:

add_filter('allowed_http_origins', function($origins) {
    $origins[] = home_url('');
    return $origins;
});

Obviously if/when the plugin is updated and this fix is not part of that update, the change will get lost. This could easily go into your theme’s functions.php file instead.