obi Cloth Version 5.6 error

[josemendez]

using System;
using System.Runtime.InteropServices;
using System.Text;
using System.Collections.Generic;
using UnityEngine;
using Unity.Collections;
using Unity.Collections.LowLevel.Unsafe;
using System.Collections;

these are already defined but it doesn't see the UnsafeUtilityEx. should I update some thing on package manager ? 

Yep. As I said, this is defined in the Collections package, so you need to install it.