title: Problem with my python API : TypeError: Object of type set is not JSON serializable
body: <p>Good morning to everyone,</p>
  <p>Well I am an alternating student and I am asked to create an API to retrieve data from their software.
  ( I don’t know much about API I discovered with an old project, so don’t judge my mistakes please ).</p>
  <p>Code :</p>
  <pre><code>try:
      infos = client.api(method='Infos.getInfos')
      clientj = client.api('Client.getList',params={
          'order':{},
          'pagination':{},
          'search':{'periodecreated_start':{int(1577836800)}
          }
      })
  except sellsy_api.SellsyAuthenticateError as e: 
      print('Authentication failed ! Details : {}'.format(e))
  except sellsy_api.SellsyError as e: 
      print(e) 
  </code></pre>
  <p>Code Erreur :</p>
  <pre><code>Traceback (most recent call last):
    File &quot;...&quot;, line 13, in &lt;module&gt;
      clientj = client.api('Client.getList',params={
    File &quot;...&quot;, line 28, in api
      'do_in': json.dumps(payload)
    File &quot;...&quot;, line 231, in dumps
      return _default_encoder.encode(obj)
    File &quot;...&quot;, line 199, in encode
      chunks = self.iterencode(o, _one_shot=True)
    File &quot;...&quot;, line 257, in iterencode
      return _iterencode(o, 0)
    File &quot;...&quot;, line 179, in default
      raise TypeError(f'Object of type {o.__class__.__name__} '
  TypeError: Object of type set is not JSON serializable
  </code></pre>
  <p>Thanks you in advance,</p>