Troubleshooting checklist for 401/403/429 errors from the ChatGPT, Claude, Gemini, and Midjourney APIs

When you hook up an automated writing workflow, a bot, and a full RAG stack, the most frustrating part isn’t mediocre results—it’s the API suddenly slapping you with 401/403/429. I’ve fallen into that trap too: the key is obviously correct, yet it still errors out, like arguing with thin air.

First, understand the three most common errors

• 401 Unauthorized: invalid key, extra spaces when pasted, or using a key from the wrong project
• 403 Forbidden: region/permission/organization policy restrictions, or your account hasn’t enabled the corresponding capability
• 429 Too Many Requests: rate limiting triggered, concurrency too high, or you’ve hit your quota or rate limit ceiling

Common causes of ChatGPT API errors

The ways I most often mess up are: having leading/trailing newlines around the key in environment variables; and thinking “it’ll work as long as it runs” when billing isn’t set up properly. When you hit 429, lowering concurrency and adding retries with exponential backoff will make the experience return to normal immediately.

Claude is more likely to get stuck on permissions

With Claude, many 403s aren’t because you wrote something wrong, but because your account/region/enterprise policy won’t allow it. A wrong model name can also make you question everything—so it’s best to double-check the model field in your request.

Gemini commonly involves quota and project configuration

If Gemini throws 429, don’t rush to blame the model—first check the project quota, call frequency limits, and whether the API corresponding to the key is enabled. Some people only create a key and forget to enable the relevant service in the console.

Midjourney is more like a Discord-side issue

Midjourney itself isn’t a traditional API flow; it’s more about Discord interactions. Common reasons it “doesn’t work” include: missing channel permissions, the bot not being in the server, incorrect command format, or being rate-limited. First confirm the bot can see your channel—that’s more reliable than repeatedly changing prompts.

My universal checking order

• Copy the key again and manually remove leading/trailing spaces and newlines
• Confirm the network environment is stable—don’t switch between direct connection and proxy
• Reduce concurrency to 1 for testing, then gradually increase it back
• Read the error fields in the response body carefully—don’t stare only at the status code

If you’re still going in circles over “invisible barriers” like subscriptions, quotas, and regional restrictions, you can check out Titikey for more detailed hands-on tutorials and tool roundups, so you’ll avoid a lot of needless detours.