404 error when posting new topic

Hi,

I’ve been trying to create a new topic in forum.
But once I try to submit a new topic/content I get a 404 page not found (redirected on page: https://www.mywebsite.com/wp-content/plugins/mingle-forum/wpf-insert.php)

BTW: I’m using Mingle-Forum(https://www.ads-software.com/support/plugin/mingle-forum) wp Plugin.

I already setup a category and forum inside it. I using the theme “dream on blue” (https://ddart-bg.com/dream-on-blue)

https://www.ads-software.com/extend/plugins/mingle-forum/