I'm stuggling with 2D animation transitions

I'm having trouble with switching between animation states for a sprite. The Parameters that I have set in the Animation Controller are: bool Grounded, bool IsWalking, and trigger IsJumping. My animations are: Idle, Walking, Falling, Jumping.

For some reason my Animations don't transition, I've tried removing certain transitions so I can get it to transition from Idle to Walking but I never see any transitions occur, sometimes I get it to start in the Falling animation because the sprite starts in the air.

I'm pretty sure I have all of my transitions set up correctly in my controller. Can someone tell me if it's a scripting mistake? Or I'm missing a step? Or Perhaps it is the Animator Controller? Anything would help, thank you.

public class PlayerCntroller : MonoBehaviour {

     //public and private floats
     public float speed;
     public float JumpForce;
 
     private Rigidbody2D rb;
 
     private bool OnGround = false;
     private float gravityScale = 0.8f;
     
 
     Animator anim;
     
     void Start () {
         rb = GetComponent<Rigidbody2D>();
         anim = GetComponent<Animator>();
     }
     
     void FixedUpdate () {
 
         bool moveL = Input.GetKey("a");
         bool moveR = Input.GetKey("d");
         bool jump = Input.GetKey("w");
 
         if (moveL == true)
         {
             Vector2 movement = new Vector2(-1, 0);
             if (OnGround == false)
                 movement = movement * 0f;
 
             rb.AddForce(speed * movement);
         }
 
         if (moveR == true)
         {
             Vector2 movement = new Vector2(1, 0);
             if (OnGround == false)
                 movement = movement * 0f;
 
             rb.AddForce(speed * movement);
         }
 
         if (OnGround == true)
         {
             gravityScale = 0;
         }
         if (OnGround == false)
         {
             gravityScale = 0.8f;
         }
 
         if (jump == true && OnGround == true)
         {
             Vector2 movement = new Vector2(0, 1);
             rb.AddForce(movement * JumpForce * 100);
         }
 
         if (Input.GetKeyDown("d"))
             transform.localScale = new Vector2(-0.25f, 0.25f);
 
         if (Input.GetKeyDown("a"))
             transform.localScale = new Vector2(0.25f, 0.25f);
 
         animator(moveL, moveR, OnGround, jump);
     }
 
     void animator(bool moveL, bool moveR, bool OnGround, bool jump)
     {
         bool m = moveL == true || moveR == true;
         bool c = OnGround;
 
         anim.SetBool("IsWalking", m);
         anim.SetBool("Grounded", c);
         if (jump == true)
             anim.SetTrigger("IsJumping");
     }
 
     void OnCollisionEnter2D(Collision2D coll)
     {
         if (coll.gameObject.CompareTag("Ground"))
         {
             OnGround = true;
         }
     }
 
     void OnCollisionExit2D(Collision2D coll)
     {
             OnGround = false;
 
     }
 }