Help me to understand please. I want to stocks (i.e. VOO). I have several thousands in cash on my account. But when I submit an order I get this message
Why does this happen? Why I can't buy when I have cash?
Maybe someone knows why my cash is blocked?
---- UPDATE -----
I found that there's a difference between Cash and Buying Power. What does it mean? 

Tradetab there are only filled and cancelled orders. Is there any other place to look at? – Yura Sep 09 '22 at 17:30