From what I see, the animation won’t play in-game, right? Might not be a scripting issue as far as I’m aware since your script works on a regular r6 dummy with the correct attributes: an Animator instance inside the model’s Humanoid (given the assumption it has one.), and an Animation instance named “Idle” under the model itself.
The explorer tab provided in the original message you sent is a little bit limited, but from what I can assume, it’s probably a problem with the model’s PrimaryPart property not being set to the RootPart. (You might also want to rename the RootPart to “HumanoidRootPart”.), or if you’re missing a few things for the script.
If that doesn’t work, send an image of the entire hierarchy in either seperate images or as a whole with all the descendants. I’m not entirely sure where you got the model from, but I’m sure it should be animatable in roblox. PS: check for any errors in the output tab and send them to me, if there are any.