I already have a margin account, and the issue is due to the number of shares (or perhaps they do not like me

). Maybe it might have something to do with taking earnings from pennies and using it to buy other pennies - but I haven't had any issues with it before.
With Zecco, your earnings add to your buying power immediately if you have a margin account. If you have a cash account, it is the regulated T+3 days. With other brokers, even if you have a margin account, you still have to wait T+3.
Technically, I believe you are somehow using margin (because if T+3 is a law and not a tradition, there's no way Zecco could get around not doing it)... but I haven't gotten dinged when holding a stock purchased via the proceeds of other stock overnight, for example (which if you normally used margin, would make interest hit if I understand Zecco's policy correctly from their message boards).
Of course, I am still trying to learn as much as I can not only about the market, but also the technicalities of things work. I know there are legitimate reasons for the T+3, but anyway.
At any rate, they directly told me that at first it is for security (I guess people breaking into accounts and randomly buying shares is a problem?), at the second it is because their risk managers don't like stuff like that (buying millions or even thousands of shares) and so they personally reject such transactions... which I can't say I agree with if you've shown that you are aware of the risks involved with pennies.