No sandbox + API No "post-only" + delay in balance update.There is no sandbox environment where to test your trading strategy. The API Explorer is just not enough.The API has no "post-only" flag for placing orders, so you can't be 100% sure that you are going to be a market maker (hence be able to get the rebate instead of paying the fee).When an order is placed (via the API at least), balances are updated with some delay, sometimes even minutes.When you place a maker order, you get substracted the fee, and when the order is filled, you get the fee reinbursed + the rebate. That seems quite odd and makes it impossible to follow your current balance.They increased the "lotSize" (the minimum order size, something not mentioned in the API docs I've read, and that value is not accessible via the API to the best of my knowledge) to 0.01 BTC some time ago, which is negative for me.After asking support (the form is impossible to find), about the fee vs rebate, I got the "you have to respect the lotSize restriction" (the order had 0.01 BTC, which is just the lotSize).Seems there are some systems issue to ge addressed yet. If HitBTC add the "post-only" flag, use a reasonable fee vs rebate logic, reduce the lotSize to 0.001 BTC, and add a sandbox environment: I'd give them 5 stars.