Collision not working

I want my player to get hit by an enemy missile, which spawns automatically. Both missile and player have rigidbodys and circular collider and are on the same layer, tags are set. This is the code I use:
void OnCollisionEnter2D(Collision2D col) { if (col.gameObject.tag == "Stein") { playerhealth -= 10; Debug.Log("HIT"); Destroy(col.gameObject); } }

Even though the player get knocked back when the missile hits him, the collision is not detected.
Any idea why it does not work and how I can fix it?

If you do not want to have force apply on Object when hit you must use OnTriggerEnter2D(Collider2D other) function instead of OnCollisionEnter2D

Be sure to have added RigidBody2D and and BoxCollider2D (or other Collider2D) on Character if you want to walk on a physic ground. Add only a BoxCollider2D( or other) on missile with the IsTrigger checked for it. No rigidbody2D on missile needed.
On Missile script add OnTriggerEnter2D function.

If you want detection on character side script the add a child object on character with Collider 2D object and IsTrigger checked. In this case I think you also need a RigidBody2D on missile.