There are two possible reasons that could be causing this issue.
It could occur when attempting to close a buy or sell position that is already closed but hasn’t updated yet due to latency issues. To troubleshoot, please log out from the terminal (MT4 or MT5) and log in again, or try to log in using a different device.
The parameters are not allowed
It also occurs when an incorrect value for lot size is input, or a price/volume isn’t set (either manually or by an EA). Keep in mind that each account type has certain limitations and ensure that you follow those to avoid this error. In that case, please ensure that your parameters fall within those set by your chosen account type.
If you are still having issues, get in touch with our Exness Support team.