Is there anything to be aware of about exchange.IO sending POST packets?

In the middle of the code, the feeling should be that there is nothing wrong, but the interface always returns a parameter that does not correspond:

function main() { exchange.IO("base", “https://api.btcgateway.pro”) //var obj = {“contract_code”:“TRX-USDT”,“volume”:10000,“direction”:“sell”,“offset”:“open”,“lever_rate”:3,“order_price_type”:“optimal_5”} var obj = {“contract_code”:“TRX-USDT”} var str = JSON.stringify(obj) Log(obj) Log(str) var hy_order_id = exchange.IO("api",“POST”, “/linear-swap-api/v1/swap_order_info”, “”, str) Log(hy_order_id) return hy_order_id }

Here are the packages returned after the call: {ts:1619326307135,status:error,err_code:1066,err_msg: The contractCode field cannot be empty. Please re-enter.}

Say I didn't pass the contract_code, but I did.