As a free trial API user, you receive an initial credit of $5 that expires after three months. Upgrading to the pay-as-you-go plan will increase your usage quota to $120/month.

If you're already a paying API customer and want to increase the monthly quota beyond the default $120, you can request a quota increase by filling out the Quota Increase Request Form. Our team will review your request and get back to you within 1-2 business days. If you don't hear from us within that timeframe, please check your spam folder or hard limit to see if your request has already been processed.

Source: https://help.openai.com/en/articles/6643435-how-do-i-get-more-tokens-or-increase-my-monthly-usage-limits