Question about buying power

[Silviu 0]

Hello! I attached below a SS of the trade I am talking about. I bought 156 shares of AAPL at 152.23 and I am trying to place a limit order of 46 shares at 152.75. However I can't seem to be able to do so. I am getting a message saying "Not enough buying power!". Can someone explain to me what I am doing wrong? Why do I need buying power to sell shares I already have? Thank you!

 

 

 

[Silviu 0]

Thanks a lot!