Cannot create order in MT5

[Matlab132]

Hi,

I wanted to build my own trading algorithm with R, I'm having a demo account from GKFX broker, using the MT5. I downloaded the MT5R package, also set up everything in MT5 and connected R to MT5 (if I use MT5.ping() I receive a TRUE).
But I cannot place an order. If I want to create a single order with the following code

MT5.SingleOrder("EURUSD",0, fVol=0.01)

It always returns a FALSE and the Expert tab in MT5 tells me

2021.10.05 13:39:28.116 mt5R v0_1_5 (EURUSD,M1) OrderSend error 4756

and if I further check in the journal tab I receive following message.

2021.10.05 13:39:28.116 Trades '17588': failed market sell 0.01 EURUSD [Unsupported filling mode]

When placing manually an order in MT5, I see the filling type is "IOC-Order" so I tried
MT5.SingleOrder("EURUSD",0, fVol=0.01, iFillType = 2)
But I received the same error messages

FYI - I applied the expoert to the specific chart and allowed algo trading, I also did a test by creating an order manually in MT5 and closing this order via R command (MT5.ClosePosition()) and this worked.

So I really don't know why I cannot create an order. Do you know what could be the issue?

Thanks and best