Sending KLAY to Contract

Just like Ethereum, you can send some KLAY to contracts. There are couple things you need to remember though.

Make sure you have fallback function with payable modifier

If you are from Ethereum, then you are probably familiar with this: to receive Ether and add it to the total balance, a contract must have fallback function marked with payable. The same rule applies to Klaytn. A contract must have one (and only one) unnamed function — a.k.a. fallback function — with payable modifier in order to receive KLAY. Without such, a contract cannot receive KLAY through regular transactions and throws an exception.

Here’s an example contract with payable fallback function:

contract WithFallbackPayable {
    event FallbackCalled(uint amount);

    function () external payable {
        emit FallbackCalled(msg.value);

Use LEGACY transaction to send KLAY

You must use LEGACY transactions when you send KLAY to contracts. Since VALUE_TRANSFER transactions are strictly allowed for KLAY transfer between EOAs, Klaytn will decline any VALUE_TRANSFER transaction if it contains a non-EOA address in to field.