Web3j transaction hash is always null with txManager

Question

code block:

TransactionManager txManager = new RawTransactionManager(web3j(), credentials());
   
 String txHash = "";
    
TransactionReceipt txReceipt;
    
    try {
        txHash = txManager.sendTransaction(
                        DefaultGasProvider.GAS_PRICE, 
                        DefaultGasProvider.GAS_LIMIT, 
                        contractAddress, 
                        encodedFunction, 
                        BigInteger.ZERO).getTransactionHash();

    } catch (IOException e) {
        e.printStackTrace();
    }


TransactionReceiptProcessor receiptProcessor = new PollingTransactionReceiptProcessor(
    web3j(), 
    TransactionManager.DEFAULT_POLLING_FREQUENCY, 
    TransactionManager.DEFAULT_POLLING_ATTEMPTS_PER_TX_HASH);

    try {
        txReceipt = receiptProcessor.waitForTransactionReceipt(txHash);
    } catch (IOException e) {
        e.printStackTrace();
    } catch (TransactionException e) {
        e.printStackTrace();
    }

Last exception returns:

org.web3j.protocol.exceptions.TransactionException: Error processing request: invalid argument 0: json: cannot unmarshal non-string into Go value of type common.Hash

I'm using a metaMask wallet and with HttpService as a public RPC enpoint for ethereum