> For the complete documentation index, see [llms.txt](https://docs.21x.eu/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.21x.eu/order-book.md).

# Smart Contract ABI

To interact with the smart contract, users must utilize the **ABI (Application Binary Interface)**, which defines the contract’s functions, input/output types, and how they are encoded for low-level interaction with the Ethereum Virtual Machine (EVM). The ABI is essential for constructing valid function calls and decoding returned data.

Access to the smart contract is **permissioned via a whitelist**. Only wallet addresses that have been explicitly authorized (i.e., added to the contract’s whitelist) are able to execute transactions or call restricted functions. Any attempt to interact from a non-whitelisted address will be rejected by the contract.

Please ensure that your wallet address is submitted for whitelisting before attempting any interaction with the contract.\
 

<figure><img src="/files/VFMzyrRPc5jE4h9rrntl" alt=""><figcaption></figcaption></figure>


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