# Book of reference

- [System IP addresses](/en/book-of-reference/ip-addresses.md)
- [Payment Form Appearance](/en/book-of-reference/payment-form.md)
- [Using the Test API](/en/book-of-reference/test-api.md)
- [Payment System Codes](/en/book-of-reference/payment-system-codes.md)
- [Currency codes](/en/book-of-reference/currency-codes.md)