0xec28438a?0xec28438a is the function selector for setMaxTxAmount(uint256). Limits the maximum transaction size.
When a transaction's data begins with 0xec28438a, it is calling setMaxTxAmount. The selector is the first four bytes of the keccak-256 hash of the signature setMaxTxAmount(uint256), which is how wallets and explorers work out which function a payload is for.