title: Docusign API "INVALID_REQUEST_PARAMETER"
body: <p>I have a problem with the DocuSign API premium plan. The first signer can sign the contract which we are generating via API without any problem, but when it comes to the second signer, in the same envelope ID we receive this error:</p>
  <pre><code>docusign_esign.client.api_exception.ApiException: (400)
  Reason: Bad Request
  HTTP response headers: HTTPHeaderDict({'Cache-Control': 'no-cache', 'Content-Length': '155', 'Content-Type': 'application/json; charset=utf-8', 'X-DocuSign-TraceToken': '6fd068b4-9f2d-41a7-bd01-351e2676f438', 'Date': 'Tue, 15 Jun 2021 08:50:45 GMT', 'Set-Cookie': 'BIGipServerpool_SE2_NA4_API=!JACGQDicHt+h1TK0bOlB09wl7Vsgf/x6uU4IHjwxIL8hJpHlxDwjr2QgIA/ku3g50UYGhRu67eFbSA==; path=/; Httponly; Secure'})
  HTTP response body: b'{&quot;errorCode&quot;:&quot;INVALID_REQUEST_PARAMETER&quot;,&quot;message&quot;:&quot;The request contained at least one invalid parameter. A value was not found for parameter \'userName\'.&quot;}'
  </code></pre>
  <p>Any help?</p>
  <p>P.S we are using:</p>
  <p>python 3.x - docusign-esign 3.10.0 SDK</p>