Problems with LineCast bettwen Camera and Objects

Hey, I'm trying to do multiple LineCast from the camera to objects to see if the objects are behind a wall but its not working!

 void CheckLineOfSight()
     {
         allEnemies.Clear();
 
         for (int i = 0; i < allEnemiesInScene.Length; i++)
         {
             //Check if Enemy is in field of view
             Vector3 cameraRelative = mainCam.transform.InverseTransformPoint(allEnemiesInScene[i].transform.position);
             screenPos = mainCam.WorldToScreenPoint(allEnemiesInScene[i].transform.position);
 
             Debug.DrawRay(mainCam.transform.position, (allEnemiesInScene[i].transform.position - mainCam.transform.position), Color.black);
 
             if (screenPos.x > 0 && screenPos.x < Screen.width && screenPos.y > 0 && screenPos.y < Screen.height && cameraRelative.z > 0)
             {
                 //Check if has an object between camera and Enemy
                 hit = new RaycastHit();

            //Not Working This Part

                 **if (Physics.Linecast(mainCam.transform.position, (allEnemiesInScene[i].transform.position - mainCam.transform.position), out hit, targetLayer))
                 {
                    //Not behind a WALL
                     Debug.DrawRay(mainCam.transform.position, (allEnemiesInScene[i].transform.position - mainCam.transform.position), Color.green);
 
              
                 }
                 else
                 {

                     Debug.DrawRay(mainCam.transform.position, (allEnemiesInScene[i].transform.position - mainCam.transform.position), Color.red);
                 }**
             }
         }
     }