error: invalid size with close-order

[witsgh]

def close_position():
if get_position_size() > 0:
# order using market price
entry_price = float(get_position_entry_price())
position_size = float(get_position_size())

    close_price = ((float(min_markup) * entry_price) + entry_price)
    last_price = get_last_price()


    if close_price > last_price:
        
        print(f"The desired close_price of {close_price} is greater than the last price of {last_price}")
    else:
        print(f"The desired close_price of {close_price} is lower than the last price of {last_price}")
       
        order = FuturesOrder(contract=contract, size='0', price='0', close='true', tif='ioc')
        try:
            
            
            order_response = futures_api.create_futures_order(settle, order)
        except GateApiException as ex:
            logger.error("error encountered creating futures order: %s", ex)
            print(f"Error: {ex}")       
    
else:
    print(f"No position found. Position size is {get_position_size()}")

Am trying to close an order with the above code, the docs says to set size='0' and close='true' but I get invalid size with close-order error. what am I doing wrong