1) Suppose I have placed the order and now it's pending and suppose from API we try to modify an order and then before modifying the order get executed then what modify order response return? is it a return an error or what? Im using golang sdk
Yes, it will return an input exception of Order cannot be modified as it is being processed. Try later. In that case, you need to refetch the order book and check the status for the same order. You can go through this thread to know more.
Order cannot be modified as it is being processed. Try later. In that case, you need to refetch the order book and check the status for the same order. You can go through this thread to know more.