I am testing futures trading via Zorro's IB API at the moment.

When I am closing trades negative prices are returned and due to this huge losses are recorded.

Below an example from the logfile:

Name,Type,Asset,ID,Lots,Open,Close,Entry,Exit,Profit,Roll,ExitType
TradeTest,Long,ES,18,1,14/06/2018 10:32.14/06/2018 10:32,2778.8,-2778.8,-277925,0,Sold

I entered and exited at the same price but a loss of $277k is shown.
Is this a common error? All it took was 5 trades and the shown demo-account size was negative.

I also tried various broker commands but could not solve it.

Can you show that script, or send it to support?

I tried various ones including TradeTest and all had the same results.

Okay, thanks I'll send it to the support.