if (mode == SettlementMode.MintBurn) {
  _erc20_lock(msg.sender, address(this), amount);
}
if (mode == SettlementMode.MintBurn) {
  _erc20_mint(
    AddressCast.to_address(transfer_payload.to),
    transfer_payload.amount
  );
  return true;
}
if (status == CrossChainMsgStatus.Success) {
  if (mode == SettlementMode.MintBurn) {
    _erc20_burn(address(this), create_cross_txs[txid].amount);
  }
  create_cross_txs[txid].status = CrossChainTxStatus.Settled;
}
if (mode == SettlementMode.BurnUnlock) {
  _erc20_burn(msg.sender, amount);
}
if (mode == SettlementMode.BurnUnlock) {
  _erc20_unlock(
    AddressCast.to_address(transfer_payload.to),
    transfer_payload.amount
  );
  return true;
}
function cross_chain_erc20_settlement(
    string memory to_chain,
    uint256 to_handler,
    uint256 to_token,
    uint256 to,
    uint256 amount
) external {
    // ...
    if (mode == SettlementMode.BurnUnlock) {
+       _erc20_lock(msg.sender, address(this), amount);
-       _erc20_burn(msg.sender, address(this), amount);
    }
    // ...
}
function receive_cross_chain_callback(
    uint256 txid,
    string memory from_chain,
    uint256 from_handler,
    CrossChainMsgStatus status,
    uint8 /* sign_type */,
    bytes calldata /* signatures */
) external onlySettlement returns (bool) {
    // ...
    if (status == CrossChainMsgStatus.Success) {
+       if (mode == SettlementMode.BurnUnlock) {
+           _erc20_burn(address(this), create_cross_txs[txid].amount);
+       }
        create_cross_txs[txid].status = CrossChainTxStatus.Settled;
    if (status == CrossChainMsgStatus.Failed) {
+       if (mode == SettlementMode.BurnUnlock) {
+           _erc20_unlock(create_cross_txs[txid].from, create_cross_txs[txid].amount);
+       }
        create_cross_txs[txid].status = CrossChainTxStatus.Failed;
    }
    // ...
}
