Get spot wallet USDT balance (Javascript)

API Spot/Margin API
1

I’ve seen a few posts on getting the balance of a particular coin, but can’t figure out how to simply get USDT balance without triggering the API limits.

The below code randomly does one of 3 things:
a) returns the right balance
b) returns empty or says there’s a illegal character returned: “<”
c) says I’ve exceeded limits and bans me for many hours <---- most common

Note that this is literally the only function I’m triggering, so there should be absolutely no reason at all to ban me. I cannot find the right endpoint to reliably return the balance.

Using Google Apps Script if that makes a difference. Any thoughts?

function getUSDTBalance(){

  var key = '______;
  var secret = '________';
  var baseUrl= "https://api.binance.com";
  //api = "/api/v3/account";

  var timestamp = Number(new Date().getTime()).toFixed(0);
  var string = "&timestamp=" + timestamp; // Please input query parameters

  var signature= Utilities.computeHmacSha256Signature(string, secret);
  signature = signature.map(function (e) {
    var v = (e < 0 ? e + 256 : e).toString(16);
    return v.length == 1 ? "0" + v : v;
  }).join("");
  var query = "?" + string + "&signature=" + signature;
  var params = {
    'method': 'get',
    'headers': { 'X-MBX-APIKEY': key },
    'muteHttpExceptions': true
  };
  var data = UrlFetchApp.fetch(baseUrl + api + query, params);
  Logger.log(JSON.parse(data));
  var j = JSON.parse(data);
  var bal = j.balances;

  var usdtBal = 0;
  for (var i = 0; i < bal.length; i++) {
    if (bal[i]["asset"] == "USDT") {
      usdtBal = bal[i].free;
      continue;
    }
  }
  Logger.log(usdtBal);
  return(usdtBal);
}