> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nexusapi.link/llms.txt
> Use this file to discover all available pages before exploring further.

# Frequently asked questions

> Find the right NexusAPI guide for setup, billing, and API errors.

When a call fails, save the Request ID and the complete error text before changing settings or retrying.

## Setup and configuration

* **Where should I start?** Read the [quick start](/en/guide/quick-start).
* **Which Base URL should I use?** It depends on the client; see the [integration overview](/en/guide/integration-overview).
* **Why do I see 404?** Check for `/v1/v1/...` and whether the client appends a path automatically.
* **Why does a new API key fail?** Check its status, credit, token group, model ID, and `Authorization: Bearer` format.

## Models and charges

* **How do I know whether a group can use a model?** Filter the [Model Marketplace](https://nexusapi.link/pricing) by the group and copy the exact ID.
* **How much did one request cost?** Use the console log and read [usage and billing](/en/billing/usage-and-billing).
* **Can an error be charged?** It can be, if an upstream request already ran or the client sent a new request. Reconcile by Request ID.
* **Why is the balance normal but the key says insufficient credit?** Check account credit, key limit, expiry, and group.

## API errors

* **What do 400, 401, 429, 500, 502, 503, 504, or 524 mean?** See [API error guide](/en/faq/common-errors).
* **Why can a long conversation no longer continue?** Save the error, start a new session, and avoid repeatedly submitting the same request.
* **Why is image generation slow or timed out?** It is synchronous. Keep the Request ID and do not immediately submit the same job again.
* **Why did an error later appear to succeed?** Do not assume the platform retried it; check client retries and matching Request IDs.

## Get help efficiently

Use the [self-check guide](/en/faq/self-check), then provide the Request ID, time and time zone, client and version, model, endpoint, full error text, and whether the issue is intermittent or persistent.

Never send a full API key, password, or private content.