This question would be if you currently have an older account that is on a “pay-as-you-go” plan, with monthly billing, using your previously-entered credit card.
If you haven’t yet received gpt-4 access (which was previously granted to accounts that had actual billings to their credit card), and want instant access, it has also been reported that you can convert your account to prepaid to also get instant gpt-4 access. And won’t be able to switch back.
Go into the account, and completely remove the payment plan at the main billing screen. You may need to logout and log back in if you don’t then see a new “add payment plan” option. Then you’ll be forced to buy credits before you can use API, with the minimum purchase.
Not recommended though. This also could have problems, many have been reported. Not taking your card due to new banking requirements, problems getting the credit due to processing bugs, the credit immediately going only to pay off your bill, for example. And of course the inconvenience of needing to pay before use and running out of credits.