title: OKEX withdraw error 10006
body: <ul>
  <li>OS: CentOS</li>
  <li>Programming Language version: PHP 5.6.35</li>
  <li>CCXT version: 1.13.49</li>
  <li>Exchange: OKEX</li>
  <li>Method: withdraw</li>
  </ul>
  
  <p>I am getting error_code 10006 from the OKEX API when attempting to make a withdrawal. Is anyone else having this issue?</p>
  
  <p>Other methods such as placing orders, checking balances etc. work fine with the exact same API key and secret. withdraw_info however also gives error 10006.</p>
  
  <p>I've checked and Withdraw privileges is definitely turned on for the API key in my OKEX account.</p>
  
  <p>I've also contacted OKEX customer support and they've been telling me to change the withdrawal symbol from btc_usd to btc_usdt, and then from btc_usdt back to btc_usd over and over for a couple of days now.</p>
  
  <p>If anyone has had the same problem please do let me know. Thank you very much in advance.</p>
  
  <p>Here is the dump from CCXT:</p>
  
  <pre><code>strong textFatal error: Uncaught exception 'ccxt\ExchangeError' with message 'okex {"result":false,"error_code":10006}' in /home/php/okcoinusd.php:721
  Stack trace:
  #0 /home/php/Exchange.php(957): ccxt\okcoinusd-&gt;handle_errors(200, '', 'https://www.oke...', 'POST', Array, '{"result":false...')
  #1 /home/php/Exchange.php(801): ccxt\Exchange-&gt;fetch('https://www.oke...', 'POST', Array, 'api_key=cff1b19...')
  #2 /home/php/Exchange.php(805): ccxt\Exchange-&gt;fetch2('withdraw', 'private', 'POST', Array, NULL, NULL)
  #3 [internal function]: ccxt\Exchange-&gt;request('withdraw', 'private', 'POST', Array)
  #4 /home/php/Exchange.php(740): call_user_func(Array, 'withdraw', 'private', 'POST', Array)
  #5 [internal function]: ccxt\Exchange-&gt;ccxt{closure}(Array)
  #6 /home/php/Exchange.php(1752): call_user_func_array(Object(Closure), Array)
  #7 /home/php/okcoinusd.php(678): ccxt\Exchange-&gt;__call('privatePostWith...', Array)
  #8 /home/p in /home/php/okcoinusd.php on line 721
  </code></pre>