i'm trying to make an fps with rigidbody but the player isn't going according to it's direction

i want to use the rigidbody for the player movement and i'm creating an fps but the rigidbody's velocity doesn't go according to the player direction

 {
     [SerializeField, Range(10f, 1000f)]
     float maxAcceleration = 100f;
     float speed = 10f;
     Vector3 desiredVelocity;
     Vector3 velocity;
     Rigidbody rigid;
     private void Start()
     {
         rigid = GetComponent<Rigidbody>();
     }
     void Update()
     {
 
         Vector3 input = new Vector3(Input.GetAxis("Horizontal"), 0f, Input.GetAxis("Vertical"));
         Vector3 direction = Vector3.ClampMagnitude(input, 1f);
         desiredVelocity = new Vector3(direction.x, 0f, direction.z) * speed;
         
     }
     private void FixedUpdate()
     {
         velocity = rigid.velocity;
 
         float maxSpeedChange = maxAcceleration * Time.deltaTime;
 
         velocity.x = Mathf.MoveTowards(velocity.x, desiredVelocity.x, maxSpeedChange);
         velocity.z = Mathf.MoveTowards(velocity.z, desiredVelocity.z, maxSpeedChange);
 
     }
 }