You set the value of animation_tree to !AnimationTree. This gets evaluated as a bool value, when you try to call the set function on the type bool, it throws an error since that type doesn’t have that function.
You need to replace !AnimationTree with $AnimationTree if you want to reference a node in the scene.
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Wow, thank you so much
Huh the tutorial code is too small that’s why i see it wrong