How to setup collision with freshly generated mesh and prefabs

The setup: There are dots(8) that spawn randomly just in front of a plane on start. The player then draws three dots with mouse-clicks. The dots connect when created, and generate a triangle(mesh) between the three dots when the third is instanced.

The desire: collision detection between the dots and the triangle. in other words, I want to award the player with the dots they've outlined with his/her three clicks and not dots outside of the triangle.

I've been reading through tutorials and answers and tried copying and pasting all sorts of code and can't get anything to trigger with the mesh. The dots will all collide (or trigger for that matter) with the plane if I ask them to, but not the mesh. They are clearly intersecting in the scene.

Is it because of the way I'm using mouse-click points in game-time to generate the mesh? perhaps I am not applying the mesh data to its collider properly? or perhaps the way to mesh just appears all the sudden it's not passing through the proper collision checks? it's going right through the dots? I am not checking isTrigger on the dots when I try collision, though on when trying OnTriggerEnter/Stay() etc. I do have a rigidbody on the dots, they do collide with the wall if I turn it's meshcollider on.

on the triangle/mesh:

     void OnCollisionEnter(Collision dot){
         Debug.Log ("collision on tri");
     }
 
     public void CreateTriangle() {
         Mesh mesh = new Mesh();
         GetComponent<MeshFilter>().mesh = mesh;
                 mesh.Clear();
         mesh.vertices = _vertices;
         mesh.uv = _UV;
         mesh.triangles = _triangles;
         mesh.normals = _vertices;
         _active = true;
         GetComponent<MeshCollider>().sharedMesh = mesh;
         
 //        MeshCollider meshc = gameObject.AddComponent(typeof(MeshCollider)) as MeshCollider;
 //        meshc.sharedMesh = mesh;
 //        mesh.RecalculateNormals();
     }

on the dots:

     void OnCollisionEnter(Collision tri) {
         Debug.Log ("Collision on" + gameObject.name + "with " + tri.ToString());
     }

Thanks for any insight. Very new to this level of programming, but if I can get this one last step to work I can get everything else rolling =D