Can not send transaction on polygon network using flutter

Question

I am using web3dart to send transaction.
I already connect wallet for polygon but can't sign transaction.
I think it's due to credential problem.

  @override
  Future<String?> sendAmount({
    required String recipientAddress,
    required double amount,
  }) async {
    final sender =
        EthereumAddress.fromHex(_connector.connector.session.accounts[0]);
    // final recipient = EthereumAddress.fromHex(address);
    final recipient = EthereumAddress.fromHex(recipientAddress);

    final etherAmount =
        EtherAmount.fromUnitAndValue(EtherUnit.szabo, (amount).toInt());
    final transaction = Transaction(
      to: recipient,
      from: sender,
      gasPrice: EtherAmount.inWei(BigInt.one),
      maxGas: 100000,
      value: etherAmount,
    );
    final credentials = WalletConnectEthereumCredentials(provider: _provider);

    // Sign the transaction
    try {
      final txBytes = await _polygon.sendTransaction(credentials, transaction);
      return txBytes;
    } catch (e) {
      print('Error: $e');
    }

    return null;
  }

This code works on ethereum network but not in polygon.