It is the sweep account. I have been in "cash" not waiting on any trades to settle. They use the term "settlement account".
OK, but I still think there is a difference between the funds showing up on your balance, and being 'settled' (available to use to purchase w/o restriction).
Example (assume non-margin account):
I have $300 cash balance in the account. I sell $1,000 worth of stock ABC. IME, as soon as I sell, my account shows a cash balance of $1,300. But that $1,000 is not 'settled' for three days.
So if I buy over $300 worth of another stock, I will be told that I cannot sell that stock until the funds from the sale of stock ABC settle.
That is my understanding. That is why I was a little surprised when the warning popped up for me, I knew I had the cash there, but alas, it was not settled cash.
Does that fit your situation? Although - I got the warning when I made the purchase (and maybe not until just after, but I'm not sure now). It would be best if it came up before it let you complete the purchase, I think mine did, but I think I hit submit rather than 'back' to check! But it worked out OK for me. Well, actually, it worked out badly, but not due to the restriction
I'll watch more closely if this comes up again. I know my balance sheet will also show 'available for purchase', and that excludes cash that is reserved against a put sale for example. But I don't think they exclude unsettled funds, as they
are available for purchase, but then there are restrictions once you make the purchase. Maybe 'available', and 'available w/o settlement restriction' would be more helpful?
-ERD50