PubSub JWT Token signing not working

Extensions
3

I’ve done some changes as you suggested but it’s still giving me the same error.
This is what i have now:

function sendContributionBroadcast(contributor) {
    console.log("sending contribution broadcast");
    const channelId = contributor.channel;
    const token = makeServerToken(channelId);
    const headers = {
        'Client-ID': i,
        'Content-Type': 'application/json',
        'Authorization': `Bearer: ${token}`
    };
    const body = JSON.stringify({
        content_type: 'application/json',
        message: JSON.stringify(contributor),
        targets: ['broadcast']
    });
    request(
        `https://api.twitch.tv/extensions/message/${channelId}`,
        {
            method: 'POST',
            headers,
            body
        }, (err, res) => {
            if (err) {
                console.log(err);
            } else {
                console.log(res);
            }
        }
    );
}

function makeServerToken(channelId) {
    console.log(`makeServerToken( channelId: ${channelId} )`);
    const serverTokenDurationSec = 60; 
    const payload = {
        "exp": Math.floor(Date.now() / 1000) + serverTokenDurationSec,
        "user_id": `${channelId}`,
        "channelId": `${channelId}`,
        "role": 'external',
        "pubsub_perms": {
            "send": ['broadcast']
        }
    };
  return jwt.sign(payload, secret);
}