first I am sorry for my English is not very good , I try my best to explain my question
I saw the Document of JForex API , the explaination of the IEngine.submitorder
I CAN NOT understand what it said below:
Parameters:
price - preferred price for order. If zero, then last market price visible on the JForex will be used. Price should be divisible by 0.5 pips or order will be rejected. In case of market orders, incorrect price (worse than current market) will be changed to current price and slippage

I just wanna to figure out what is "divisible by 0.5 pips or order will be rejected"
if there's a EUR/USD ask price like 1.40723 OR 1.40730
so 1.40723 will be rejected because 1.4072 +0.00003 can not be divisible by 0.5pips
and 1.40730 will be excuted because 1.4072 + 0.00010 can be divisible by 0.5pips
is that correct?
but if 1.40723 is now current best price , I want to open a BUY position , because the strange reason of "price should be divisible by 0.5 pips"
my request will be rejected , and I can only get the 1.40730 price for my BUY order
is that correct?

could you explain why "price should be divisible by 0.5 pips or order will be rejected"?
thank you very much

如果你可以讀中文，可以解答我的問題嗎？
為什麼我開買倉還要「價格可以被0.5 pips整除」
如果不能整除，我要求的訂單就會被退回？
這是什麼規則？聽都沒聽過

Yes, your reasoning is correct. However, the new minimum increment of order price is 0.1 pips, the documentation will be updated with the next API release.
This is a restriction set by JForex platform server - currently the server works with prices with maximum 5 decimal places (i.e. this resembles the 0.1 pip increment requirement).