Keep getting Timestamp error on Coinbase API Call - authentication

Question

I'm trying to connect my Google Sheet to Coinbase API using apps script. When I try to use the authentication with my keys, I keep getting the same error:
{"errors":[{"id":"authentication_error","message":"invalid timestamp"}]}
(Code 401).
I try to check the time difference between my request and Coinbase server (to see if it is more than 30 seconds) and it doesn't. (1589465439 (mine) / 1589465464 (server)).
My code:
var timestamp = Math.floor(Date.now() / 1000) + 15;
Logger.log(timestamp);
var req = {
method: 'GET',
path: '/v2/accounts',
body: ''
};
var message = timestamp + req.method + req.path + req.body;
var secret = Utilities.base64Decode(apiKey);
secret = Utilities.newBlob(secret).getDataAsString();
//create a hexedecimal encoded SHA256 signature of the message
var hmac = Utilities.computeHmacSignature(Utilities.MacAlgorithm.HMAC_SHA_256, message, secret);
var signature = Utilities.base64Encode(hmac);
Logger.log(signature);
var signatureStr = '';
for (i = 0; i < signature.length; i++) {
var byte = signature[i];
if (byte < 0)
byte += 256;
var byteStr = byte.toString(16);
// Ensure we have 2 chars in our byte, pad with 0
if (byteStr.length == 1) byteStr = '0' + byteStr;
signatureStr += byteStr;
}
Logger.log(signatureStr);
var options = {
baseUrl: 'https://api.coinbase.com/',
url: req.path,
method: req.method,
headers: {
'CB-ACCESS-SIGN': signatureStr,
'CB-ACCESS-TIMESTAMP': timestamp,
'CB-ACCESS-KEY': apiKey
}
};
var response = UrlFetchApp.fetch("https://api.coinbase.com/v2/accounts", options);

Answer 1

This is an old question, but in case it's still unsolved, I see a few changes that will fix this. I ran into a similar issue and had to solve it.
You should have 2 keys total (1 API key, 1 secret Key). Secret key is a separate key that comes from Coinbase, and is not a decoded variant of the API access key. It does not need explicit decoding.
Where you're passing timestamp as a header -> convert that value to a string to fix the timestamp error.
headers: {
'CB-ACCESS-SIGN': signatureStr,
'CB-ACCESS-TIMESTAMP': timestamp.toString(),
'CB-ACCESS-KEY': apiKey
}
You can collapse the hmac and signature variables into this one liner before converting to hex.
let signature = Utilities.computeHmacSha256Signature(message, secret);
These 3 changes make your code start to work with my keys.