For no rhyme or reason that I can define some buy orders are rejected. All order values are the same, in this case $3,043 AUD. Orders are submitted serially. The image shows the first two orders rejected with later orders accepted. There is plenty of cash.
These buy orders are MKT GTC and sent after hours.
Trader Workstation also denies the orders so the IB Controller is in the clear. Let me continue if I may:
Fiddling with the settings I can submit LMT GTC & LMT DAY for the orders previously rejected using MKT GTC.
All orders are accepted if submitted using LMT. Is it that IB has a rule constraining after hours MKT orders in some way?