How do I make my animations work in-game and in studio?

I was using some animations I got from the devfourm on some guns I found and the animations work in studio, but when I actually play the game they just don't load in at all.

When using animations, you should refer to HAT:

• HumanoidRootPart
• AnimationPriority
• TrackUsed

Where:

• The HumanoidRootPart must be unanchored. This is a no-brainer if you're playing the animation on the player, but if you're playing it on a dummy rig instead you have to unanchor its HRP.
• Make sure the AnimationPriority is set to Action, or else it will likely not play correctly.
• Use the AnimationTrack of the Animation, not the Animation itself. Humanoid:LoadAnimation() is a function that returns the AnimationTrack of the given Animation instance.

Per quota:

"Do you own the animations themselves? As in the animations are on your inventory on the website. If you, the game creator, or the group, that owns the game, doesn't own the animations they won't work in game."

This is incorrect. Any developer can use any animation they want, including animations not created by Roblox or the developer. Nothing prevents you from using said animations.