[How to show player health (number) under their name]

Ive tried showing player health under their name but for some reason it wont work.
If i try to show health on the sidebar, it works.

How do I fix this?

[World uploaded but when I join its just a regular world.]

Ok Ive tried to get a link to the world, and Its only 353 mb which is under 500 so i dont know what the problem is. Can anyone help me?

[World uploaded but when I join its just a regular world.]

The only problem i can think of is if i did something wrong or the file is just too big

[World uploaded but when I join its just a regular world.]

When i do /worlds all i get is nether end and the normal world

[World uploaded but when I join its just a regular world.]

I uploaded a world to my server called "Skyblock remake map v1.0" and when I upload it, I don't get any errors. I restart my server, join, and it isn't there. I just get a random seed. The world is really big, has lots of command blocks, and it's a huge file, but since I don't receive any errors, I don't know why it won't work. Can anyone help?