blockchain.com saying I do have enough funds I have had 0.3097 of a BTC in a wallet for a couple of years. Needing to pay for something, I went into blockchain.com and entered the login link and password and the system showed me the balance which was correct. So far so good.

I then called up SEND and entered the balance (I want to send all the money in the wallet to a certain address). No matter what I enter in the amount box, red letters come up saying "insufficient funds".

What do I do ?
When you click send a modal window pops up. Look at the transaction fee in the bottom right of that. Deduct that from your balance and you'll be able to move your bitcoins.