Raycast not visible

Hey everyone, Im making an RTS and im trying to begin by having a raycast able to be visible on click so that i can detect if a unit is being selected by the mouse (if there is an easier way let me know). Anyways, its not showing up, and I feel ive tried about everyting. Here is my code below:

 if (Input.GetMouseButtonDown (0)) { //if left click...
             startClick=Input.mousePosition; //give the position
 
             //test code
             Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition); //trying to single select
             RaycastHit hit;
             
             Debug.DrawRay (ray.origin, startClick * Mathf.Infinity, Color.red);
             
             if (Input.GetMouseButtonDown (0)) {
                 
                 if(Physics.Raycast(ray,out hit, Mathf.Infinity)){
                     //startClick=hit.point;
                 }
                 
                 
             }