WordPress won’t accept slug name, keeps changing it

That means that there is a page/post/something that uses that URL slug already. What that is… may be hard to tell without digging in the database. If you looking there you’ll see in the wp_posts table and search in the ‘post_name’ column you should be able to find what it is.

But, that URL is also redirected to the homepage somehow. That could be something in your WordPress site, in the .htaccess file, or n some other way in your hosting account. You should get that sorted out before you do anything else.