Visual Studio Code – Error C# (CS0246) while implementing an interface in a class in Unity

I’m getting acquainted with the Polymorphism of OOP while making a game in Unity.

I try to use an interface that will take part in a damage system.

Here is the interface code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public interface IDamageable 
{
    int Health { get; set;}
    void Damage();
}

And here is the code of a skeleton enemy, who inherits from the parent class Enemy and has to implement the IDamageable interface:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Skeleton : Enemy, IDamageable
{
    public int Health { get; set; }

    public override void Init()
    {
        base.Init();
        Health = base.health;
    }

    public void Damage()
    {
    }
}

So the thing is that the console in Unity doesn’t show any error messages regarding the interface.

But the VS Code keeps the IDamageable underlined with an error CS0246:

The type or namespace name ‘IDamageable’ could not be found (are you missing a using directive or an assembly reference?)

Looks like VS Code doesn’t even see the interface – can’t find the interface in intellisense either.

I tried to implement the interface for some other enemies, but the case is the same: no error in the unity console, and the interface is also marked by VS Code.

Sorry if that question is dumb!