2D Raycasting to detect if a player isGrounded

Hy everybody,
In my 2D game plateform, I want to check if my player is on the ground. For this, I use this code in my FixedUpdate() method:

    void FixedUpdate(){
   RaycastHit2D hit=Physics2D.Raycast(transform.position,-Vector.up,velocity.y);
   if(hit.collider!=null){
   isGrounded=true;
  }
}

As a result, the Raycast function returns my own player collider2D. I’ve tried with layers but doesn’t work (I added a tag and assigned it to the plateform, added the LayerMask.NameToLayer(“plateforms”) as an argument to my method and I had the same result).
Do you know how to send the exact Ray (what are the rights arguments of origins, direction and distance)?
Thanks in advance

You need to set the ‘Layer’ instead of the ‘Tag’.

Also if you make your layer mask a public variable then you can set it in the editor using a drop down menu which can be very useful.