The nicknames are working. That is not the problem. It's the names. Most of my horses have numbers for names because Horse Eden's renamer doesn't work. It only works for some of my horses. SO FRUSTRATING!

It's probably because the names your trying to use are already taken

^^^ This.

If the name is already in use by someone else, it will not allow you to use it.

I'd suggest coming up with different names, or maybe slightly changing the spelling.

You can use some letters or kind of a prefix, too - so you can use the same horse name multiple times.

e.g. if "Luna" will not work, you could try "M. Luna" or "§ Luna" and so on ;)