New Developer - Unsure how to Integrate API

whats not working whats the error returned?

In the past I have avoided async and used

    fetch(
        'https://api.twitch.tv/helix/users?id=' + twitch_id,
        {
            method: 'GET',
            headers: {
                'Accept': 'application/json',
                'Client-ID': client_id
            }
        }
    ).then(response => response.json()
    ).then(response => {
    }).catch(err => {
        // hmm
        console.log(err);
    });

In an extension