When creating an order, the bot fee is held by the smart contract in order to pay the keeper bot when the order gets executed.
As such, you need to approve the smart contract to spend your USDC. This is similar to the ERC-20 token approvals for other smart contract. We allow users to approve as much or as little as they wish, and would recommend setting the approval as low as necessary for the orders they wish to create.
For example, Charlie wishes to create 10 orders, with each order having a bot fee of $0.20. He should therefore set the approval to $2 to allow him to create these orders.