# Page Not Found

The URL `files/NUJ9LXfawANYAF0ZlvMU` does not exist. This page may have been moved, renamed, or deleted.

## Suggested Pages

You may be looking for one of the following:
- [I. Lời mở đầu](https://prepedu.gitbook.io/prep-help-center/i.-loi-mo-dau.md)
- [II. Các quy định/quy phạm trình bày trong tài liệu](https://prepedu.gitbook.io/prep-help-center/ii.-cac-quy-dinh-quy-pham-trinh-bay-trong-tai-lieu.md)
- [III. Hướng dẫn kích hoạt mã/gia hạn sản phẩm Prep](https://prepedu.gitbook.io/prep-help-center/iii.-huong-dan-kich-hoat-ma-gia-han-san-pham-prep.md)
- [6. Study Plan](https://prepedu.gitbook.io/prep-help-center/iv.-huong-dan-su-dung-cac-san-pham-tinh-nang/6.-study-plan.md)
- [IV. Hướng dẫn sử dụng các sản phẩm/tính năng](https://prepedu.gitbook.io/prep-help-center/iv.-huong-dan-su-dung-cac-san-pham-tinh-nang.md)

## How to find the correct page

If the exact page cannot be found, you can still retrieve the information using the documentation query interface.

### Option 1 — Ask a question (recommended)

Perform an HTTP GET request on the documentation index with the `ask` parameter:

```
GET https://prepedu.gitbook.io/prep-help-center/i.-loi-mo-dau.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

### Option 2 — Browse the documentation index

Full index: https://prepedu.gitbook.io/prep-help-center/sitemap.md

Use this to discover valid page paths or navigate the documentation structure.

### Option 3 — Retrieve the full documentation corpus

Full export: https://prepedu.gitbook.io/prep-help-center/llms-full.txt

Use this to access all content at once and perform your own parsing or retrieval. It will be more expensive.

## Tips for requesting documentation

Prefer `.md` URLs for structured content, append `.md` to URLs (e.g., `/prep-help-center/i.-loi-mo-dau.md`).

You may also use `Accept: text/markdown` header for content negotiation.