Need help with Rig in Unity!

Hey there!

I'ma involved in a project about a simple videogame to learn how to use Blender and Unity. The main character is a dice-head monkey.
I rigged the figure whith Rigify (adding more bones and IKs such the tail's ones), animated it and then expoted it to FBX format to use it in Unity.
Once in Unity, I set it as a 'Humanoid' rig (because it is humanoid, despite the tail). Immediately the following warning appeared: "Invalid Avatar Rig Confiuration. Missing or invalid transform: Required human bone 'Head' not found".

But, as you can see in the image bellow, the armature in Blender does have a bone called 'head' (which is completely operative), so I dont know why is this happening.

Does anybody know how to fix it?
Thank you inadvance!