Climbing small stairs with addForce doesn't work as expected

I can climb a slope but still slide off it a bit and can't climb stairs at all. I know this is mostly my code but, like I said in the title, I only want to know the logic behind why it doesn't work. Tell me if you need more parts of the code, I didn't want to put too much here.

using System.Collections.Generic;
using UnityEngine;

public class CharacterMovement : MonoBehaviour
{
    //Variables 
    [Header("PlayerStairsClimbing")]
    [SerializeField] GameObject lowerRay;
    [SerializeField] GameObject higherRay;
    [SerializeField] float stepHeight = 0.3f;
    [SerializeField] float stepSmooth = 0.1f;

public void Awake()
    {
        higherRay.transform.position = new Vector3(higherRay.transform.position.x, stepHeight, higherRay.transform.position.z);
    }
//Called once per fixedFrame
private void FixedUpdate()
    {
        //calls function
        StepClimb();
    }

private void StepClimb()
    {
        if (Physics.Raycast(transform.position - new Vector3(0, .6f, 0), orientation.transform.TransformDirection(new Vector3(0, -1, 1).normalized), .6f))
        {
            rb.AddForce(new Vector3(0f, 6f, 0f));
        }
    }
}