Why are my leaderstats not saving?

When I change leaderstats using a localscript, it changes them but when I add or remove from them they change back to their original value.

For example, I have a leaderstat called "Cash" and the value is 0. I increase it to 999999999 with a localscript. I add 1 to them using a script (not localscript) and it changes to 1.

Why can only scripts change leaderstats and not localscripts? Is there a fix for this?