Funding
This account holds paper cash. Money you add here is not real money, and the venue moves it the same way it will move funds later: it books the change, answers with your new balance, and turns down anything it cannot do.
Deposit
Add paper cash to this account. The venue credits it and answers with the balance you now hold.
Withdraw
Take paper cash back out. Ask for more than you hold and the venue turns the request down, so your balance stays where it was.