Add Credit Balance in OpenAI

Log in at https://platform.openai.com/login.

Click Settings (top right corner).

Go to Billing in the left-hand menu.

Click Add to credit balance. (If you have not setup the payment method, the button will show Add payment details)

Select the amount and payment method, then click Continue.

Click Confirm Payment.

(Optional) You can also enable Auto-recharge so your credits top up automatically in the future.