PlayPauseAudioSource.cs

using UdonSharp;
using UnityEngine;
using VRC.SDKBase;
using VRC.Udon;

public class PlayPauseAudioSource : UdonSharpBehaviour {
    public AudioSource audio;

    private bool hasPlayed = false;

    public override void Interact() {
        if (this.audio == null) {
            Debug.Log("The audio has not set.");
            return;
        }

        if (!this.hasPlayed) {
            this.audio.Play();
            this.hasPlayed = true;
            return;
        }

        if (this.audio.isPlaying) {
            this.audio.Pause();
            return;
        }

        this.audio.UnPause();
    }
}