Confused with animations

I know this question has been asked, but how do developers succeed to let their animation be able to play in a game?

Like, I remember one time I created a crawling animation using a crawling animation and a script to toggle it, and give it to my friend for contribution, then she said it’s not working. I’m confused about why.

So my question is, how can I always make sure whenever I create an animation, it will be able to play and replicate to all clients when in a game so that when like an animation(for example walking) is playing and making sure that the client sees it?

Really depends if you use a custom character, Ive found that even slight changes to the character can totally throw off a animation, try including a body model that works with each animation for comparison to ensure they work

I’m not asking that, I asked:

regardless of what rig or model is.