def sell(self, account_id, **params):
        """https://developers.coinbase.com/api/v2#sell-bitcoin"""
        if 'amount' not in params and 'total' not in params:
            raise ValueError("Missing required parameter: 'amount' or 'total'")
        for required in ['currency']:
            if required not in params:
                raise ValueError("Missing required parameter: %s" % required)
        response = self._post('v2', 'accounts', account_id, 'sells', data=params)
        return self._make_api_object(response, Sell)
https://developers.coinbase.com/api/v2#sell-bitcoin