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This is the contract that resides in a privacy group:

pragma solidity 0.7.4;

import "./Coin.sol";

contract PrivateTransfer {

    Coin coin;

    constructor(Coin _coin) {
        coin = _coin;
    }

    function transfer(address from, address to, uint amount) external {
        coin.subBalance(from, amount);
        coin.addBalance(to, amount);
    }

    function getBal() external view returns (uint) {
        return coin.getBalanceOfCB();
    }
}

And, this is the public smart contract:

import "./SafeMath.sol";

contract Coin {

    using SafeMath for uint256;

    mapping(address => uint) private balances;

    // some more code here

    function addBalance(address bank, uint amount) external {
        balances[bank] = balances[bank].add(amount);
    }

    function subBalance(address bank, uint amount) external {
        require(balances[bank] >= amount, "Insufficient balance.");

        balances[bank] = balances[bank].sub(amount);
    }

    function getBalanceOfCB() external view returns (uint) {
        return balances[auth.centralBankAddress()];
    }

    function issue(uint amount) external {
        balances[msg.sender] = balances[msg.sender].add(amount);
    }

}

Finally, here is my web3j code:

final ContractGasPrice contractGasPrice = new ContractGasPrice();
final BesuPrivacyGasProvider besuPrivacyGasProvider = new BesuPrivacyGasProvider(BigInteger.ZERO);

final Credentials CENTRAL_BANK = Credentials.create("8f2a55949038a9610f50fb23b5883af3b4ecb3c3bb792cbcefbd1542c692be63");
final Credentials ALPHA_BANK = Credentials.create("c87509a1c067bbde78beb793e6fa76530b6382a4c0241e5e4a9ec0a0f44dc0d3");
final Credentials OMEGA_BANK = Credentials.create("ae6ae8e5ccbfb04590405997ee2d52d2b330726137b875053c36d94e974d162f");

final Base64String ENCLAVE_KEY_CENTRAL_BANK = Base64String.wrap("ApXYaIWJ8Mfm18YPHNdWLfZfdttcxfXPGOmKyshsC3g=");
final Base64String ENCLAVE_KEY_ALPHA_BANK = Base64String.wrap("vyGLN7JpYuk04z/aWlHIdAHXcdBj0I1F/BVlEEElSiU=");
final Base64String ENCLAVE_KEY_OMEGA_BANK = Base64String.wrap("pAjuacbr+85FEy4/f56k81CaJ2nwsm8GgqywzQPaM1w=");

Besu nodeCentralBank = Besu.build(new HttpService("http://localhost:8545"));
Besu nodeAlphaBank = Besu.build(new HttpService("http://localhost:8546"));
Besu nodeOmegaBank = Besu.build(new HttpService("http://localhost:8547"));

Web3j web3j = Web3j.build(new HttpService());

// Create a privacy group
final Base64String privacyGroupId = nodeCentralBank.privCreatePrivacyGroup(Arrays.asList(ENCLAVE_KEY_CENTRAL_BANK, ENCLAVE_KEY_ALPHA_BANK), "bankA_bankB", "desc").send().getPrivacyGroupId();
System.out.println("Privacy Group created with Id: " + privacyGroupId.toString());

PrivateTransactionManager transactionManagerBankA = new BesuPrivateTransactionManager(nodeCentralBank, besuPrivacyGasProvider, CENTRAL_BANK, Long.decode("0x7e2"), ENCLAVE_KEY_CENTRAL_BANK, privacyGroupId);

// Deploy the public contracts
System.out.println("Deploying Contracts...");
Auth auth = Auth.deploy(web3j, CENTRAL_BANK, contractGasPrice).send();
Coin coin = Coin.deploy(web3j, CENTRAL_BANK, contractGasPrice, auth.getContractAddress()).send();

// Deploy the private contract
PrivateTransfer privateTransferBankA = PrivateTransfer.deploy(web3j, transactionManagerBankA, besuPrivacyGasProvider, coin.getContractAddress()).send();

// Perform the transfers
System.out.println(coin.issue(BigInteger.TEN).send());  // works
System.out.println(coin.getBalanceOfCB().send());   // works
System.out.println("PT Bal: " + privateTransferBankA.getBal().send());  // fails
System.out.println(privateTransferBankA.transfer(CENTRAL_BANK.getAddress(), ALPHA_BANK.getAddress(), BigInteger.ONE).send());  // fails
System.out.println("PT Bal: " + privateTransferBankA.getBal().send());  // fails

The lines commented with fails doesn't run and throw this error:

Transaction null has failed with status: 0x0. Gas used: unknown. Revert reason: '0x'.

I ran the contracts on Remix and there they work fine. But, of course, I couldn't test the privacy group aspect of this. Can anyone please point what is that I am missing or is there something wrong with the web3j library?

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