Vector3.SmoothDamp has some invalid arguments

I have a set of code like so:

 using UnityEngine;
 using System.Collections;
 
 public class SkyboxCamera : MonoBehaviour {
     
     public Transform otherCamera;
     public bool damp = false;
     public float smoothTime = 2.0f;
     public Vector3 velocity = Vector3.zero;
 
     void FixedUpdate () {
         otherCamera = Camera.main.transform;
 
         if (!damp) {
             transform.rotation = otherCamera.rotation;
         } else if (damp) {
             transform.rotation = Vector3.SmoothDamp(transform.rotation, otherCamera.rotation, ref velocity, smoothTime);
         }
     }
 }

For some reason every time I'm getting a error where the Vector3.SmoothDamp is at that says:

The best overloaded method match for `UnityEngine.Vector3.SmoothDamp(UnityEngine.Vector3, UnityEngine.Vector3, ref UnityEngine.Vector3, float)' has some invalid arguments

What am I doing wrong? Im following the documentation for Vector3.SmoothDamp and everything looks fine to me. Am I missing something?