What does a 429 error mean when using an AI API and how do I fix it?

A 429 means "too many requests" and has two very different causes: you are sending requests or tokens faster than your limit allows, or you have run out of credit or hit a spending cap. OpenAI's help center describes both under 429, so read the error body to see which.

How to handle it:

1. If it is a rate limit, slow down, add retries with exponential backoff, and respect any Retry-After header.
2. Reduce tokens per request by trimming prompts.
3. Spread work out with a queue instead of firing everything at once.
4. If it is a quota or billing message, retrying will not help. Add credit or raise the spend limit in your account.
5. Remember that a chat subscription and API billing are usually separate things.

Why it happens: providers limit traffic per account to keep the service fair. Limits differ by account and change, so check your dashboard for the numbers that apply to you.