If you see the following message while trading "The maximum remaining quantity for long positions with this instrument is 0", the reason will be a restriction for maximum traded quantity.
Currently, a large number of CFDs on stocks has limited trading quantity. The reason for that being the stock market is one-directional and given that CFDs are leveraged, there are limits to our exposure.
There are no limits on investing with real stocks with zero commission whatsoever with our Invest service.