404 Page Not Working

We have had to change categories and move galleries in order to clean up our site, but the problem is when our customers visit to pay for their order from a previous link they get the following message.  WE have edited our custom 404 page and we were expecting it to show up to redirect them to the home page so they can find their page by navigating the home page.  How do we get our 404 page to show up for the broken links?

Not Found

The requested URL was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

It is working now. I needed to tweak the .htaccess file.

Thank you !!.  Unfortunately we have to move our categories to another category so there will be numerous broken links.  I love that this has a link to the home page so our clients can find the page for themselves.  Is there a way to create a redirect from the boken link to the correct link for the gallery.

For example our current set up is top Category Highschools. and a sub category for each HIgh school with a sub category for each sport.  Within Each Sub category Lies the galleries for the team and individual images. 

Because we have added Middle schools and Private schools that have both Middle and high school grades.  We decided that we really need a category above the High school level that says Schools. ( everything would fall under that). I know I have to do it manually.  However if we don't then our home page will have numerous links on the menu page.  When we do that we will have broken links for all of those Galleries.  Is there away to redirect each gallery to the new url which is the same url except it will have the school category first?

You would need to email me the old link and the new link to forward to in this format for every gallery: 

The links at the links after the domain name. Example https://site.domain.com/galleries/scool/gallery-name/