> For the complete documentation index, see [llms.txt](https://help.unitpay.ru/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.unitpay.ru/en/book-of-reference.md).

# Book of reference

- [System IP addresses](https://help.unitpay.ru/en/book-of-reference/ip-addresses.md)
- [Payment Form Appearance](https://help.unitpay.ru/en/book-of-reference/payment-form.md)
- [Using the Test API](https://help.unitpay.ru/en/book-of-reference/test-api.md)
- [Operator Codes](https://help.unitpay.ru/en/book-of-reference/operator-codes.md)
- [Payment System Codes](https://help.unitpay.ru/en/book-of-reference/payment-system-codes.md)
- [Currency codes](https://help.unitpay.ru/en/book-of-reference/currency-codes.md)
- [Qiwi Country Codes](https://help.unitpay.ru/en/book-of-reference/qiwi-country-codes.md)