code: def in_chain(cls, client, chain_id, expiration_dates=[]):
          
  
          request_url = "https://api.robinhood.com/options/instruments/"
          params = {
              "chain_id": chain_id,
              "expiration_dates": ",".join(expiration_dates)
          }
  
          data = client.get(request_url, params=params)
          results = data['results']
  
          while data['next']:
              data = client.get(data['next'])
              results.extend(data['results'])
          return results
docs: fetch all option instruments in an options chain
          - expiration_dates = optionally scope