I know when I set up my account with Etrade, the first amount you send, has to sit for 3 days. They want that $ to clear the bank, since there's no equity in shares yet. I know that I can transfer $ to my Etrade account, without having the $ in my bank. So I suppose, they have to do that with whoever you trade with. They don't want you trading with $ you don't have. Once you have equity in shares, the $ will be able to be used. Up to the value of your shares value. Hope this makes sense.
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