please help, how do i imput a valid Limit btc on coinbase?

[Dummy55]

Hi everyone, how do i imput a valid Limit btc trade on coinbase?  What form do I right it in?  I tried everything. .1, 0.1,   0.100000, 0.0100000000.  Every time I try it says invalid amount.  Currently on hold for 30 min.  Thank you in advance for anyone that helps out.  I feel like such an idiot.