How do I make my player jump only once a frame?

using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Diagnostics;
using UnityEngine;

public class Player : MonoBehaviour
{
    private bool JumpKeyWasPressed;
    private float HorizontalInput;
    // Start is called before the first frame update
    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            JumpKeyWasPressed = true;
        }
        HorizontalInput = Input.GetAxis("Horizontal");

    }
    void FixedUpdate()
    {
        if (JumpKeyWasPressed)
        {
            GetComponent<Rigidbody>().AddForce(Vector3.up * 5, ForceMode.VelocityChange);
            JumpKeyWasPressed = false;
        }
    }
}