I have the Blockchain app on my iPhone that I've used regularly for years but actually haven't used in 2 months. It currently holds around $81 worth of BTC in my private wallet. Now I'm trying to send the $81 from my wallet. I click Send, select Private Key Wallet, enter the recipient's address but when I type in $50 it shows me in red that I'm trying to send an amount over my limit. Can anyone tell me what's going on with this?