Blockchain – Bitcoin says it will send over limit

I have a blockchain app on my iPhone that I’ve used regularly for several years but haven’t actually used in the past two months. I currently have about $81 worth of BTC in my personal wallet. Now I’m trying to take $81 out of my wallet. I clicked Send, selected my private key wallet, and entered the recipient’s address, but when I entered $50, it said in red that I was trying to send over the limit. Can anyone tell me what’s going on?