title: What is echostr in Lbank api?
body: <p>I want use Lbank api in php language. What is <code>echostr</code>?</p>
  <p>According to Lbank docs: <a href="https://docs.lbkex.net/en/#authentication" rel="nofollow noreferrer">https://docs.lbkex.net/en/#authentication</a></p>
  <blockquote>
  <p><code>echostr</code>: the param is digit or letter，length is from 30 to 40. You can directly use echostr of SDK, it's safe.</p>
  </blockquote>
  <p>How can I create <code>echostr</code> in php?</p>