Help with Mesh and Armature parenting (Bone heat error)

Hello there.

I’ve got a model to rig for Unity and I did the whole armature manually, and when I try to parent it, it gives me an error about Bone heat weightnig. I tried removing duplicates, applying the rot & scale and nothing really works.

I was following a youtube tutorial and got kinda stuck, so any help would be greatly appreciated.

Here is the .blend file: