There are three reasons you might receive the "You've reached your usage limit" error:
If you're using a free trial account: To set up a pay-as-you-go account using the API, you'll need to enter billing information and upgrade to a paid plan.
If you're already on a paid plan, you may need to either increase your monthly budget. To set your limit over the approved usage limit (normally, $120.00/month) please review your Usage Limits page for information on advancing to the next tier. If your needs exceed what's available in the 'Increasing your limits' tier or you have an unique use case, click on 'Need help?' to submit a request for a higher limit. Our team will look into your request and respond as soon as we can.
Why did I get charged if I'm supposed to have free credits?
Free trial tokens to API users on platform.openai.com are only given the first time you sign up then complete phone verification during the first API key generation. No accounts created after that will receive free trial tokens.