        require(amount > 0, "Amount must be greater than 0");
        require(to != 0, "Invalid to address");
        require(to_handler != 0, "Invalid to handler address");
        require(to_token != 0, "Invalid to token address");
        fn cross_chain_erc20_settlement(ref self: ContractState, to_chain: felt252, to_handler: u256, to_token: u256, to: u256, amount: u256) -> felt252{
            assert(self.support_handler.read((to_chain, to_handler)), 'not support handler');
            let settlement = IChakraSettlementDispatcher {contract_address: self.settlement_address.read()};
            let from_chain = settlement.chain_name();
            let token = IERC20Dispatcher{contract_address: self.token_address.read()};
            let token_burnable = IERC20MintDispatcher{contract_address: self.token_address.read()};
            if self.mode.read() == SettlementMode::MintBurn{
                token.transfer_from(get_caller_address(), get_contract_address(), amount);
            }else if self.mode.read() == SettlementMode::LockMint{
                token.transfer_from(get_caller_address(), get_contract_address(), amount);
            }else if self.mode.read() == SettlementMode::BurnUnlock{
                token_burnable.burn_from(get_caller_address(), amount);
            }else if self.mode.read() == SettlementMode::LockUnlock{
                token.transfer_from(get_caller_address(), get_contract_address(), amount);
            }
            
            ---SNIP---
        }
+       assert(amount > 0, 'Amount must be greater than 0');
+       assert(to != 0, 'Invalid to address');
+       assert(to_handler != 0, 'Invalid to handler address');
+       assert(to_token != 0, 'Invalid to token address');
