How to use the exonum-client.hexadecimalToUint8Array function in exonum-client

const buildMessage = (header, body, keyPair) => {
  const unsignedMessage = appendBuffer(new Uint8Array(header), body)

  // calculate payload and insert it into buffer
  Exonum.Uint32.serialize(unsignedMessage.length + SIGNATURE_LENGTH, unsignedMessage, PAYLOAD_SIZE_OFFSET)

  // calculate signature
  const signature = Exonum.sign(keyPair.secretKey, unsignedMessage)

  // append signature to the message
  return appendBuffer(unsignedMessage, Exonum.hexadecimalToUint8Array(signature))
}

transfer (keyPair, receiver, amountToTransfer, seed) {
        // Describe transaction
        const transaction = new TransferTransaction(keyPair.publicKey)

        // Transaction data
        const data = {
          seed: seed,
          toWallet: Exonum.hexadecimalToUint8Array(receiver),
          sum: amountToTransfer
        }

        // Send transaction into blockchain
        return transaction.send(TRANSACTION_URL, data, keyPair.secretKey)
      },

transfer (keyPair, receiver, amountToTransfer, seed) {
        // serialize and append message header
        const header = createHeader(TX_TRANSFER_ID)

        // serialize and append message body
        const data = {
          seed: seed,
          senderId: Exonum.hexadecimalToUint8Array(keyPair.publicKey),
          recipientId: Exonum.hexadecimalToUint8Array(receiver),
          amount: amountToTransfer
        }
        const body = TransferTransactionProtobuf.encode(data).finish()

        return axios.post(TX_URL, buildMessage(header, body, keyPair))
          .then(response => waitForAcceptance(keyPair.publicKey, response.data))
      },

transfer (keyPair, receiver, amountToTransfer, seed) {
        // serialize and append message header
        const header = createHeader(TX_TRANSFER_ID)

        // serialize and append message body
        const data = {
          seed: seed,
          senderId: Exonum.hexadecimalToUint8Array(keyPair.publicKey),
          recipientId: Exonum.hexadecimalToUint8Array(receiver),
          amount: amountToTransfer
        }
        const body = TransferTransactionProtobuf.encode(data).finish()

        return axios.post(TX_URL, buildMessage(header, body, keyPair))
          .then(response => waitForAcceptance(keyPair.publicKey, response.data))
      },

createWallet (keyPair, balance) {
        // serialize and append message header
        const header = createHeader(TX_WALLET_ID)

        // serialize and append message body
        const data = {
          ownerPublicKey: Exonum.hexadecimalToUint8Array(keyPair.publicKey),
          initialBalance: balance
        }
        const body = CreateTransactionProtobuf.encode(data).finish()

        return axios.post(TX_URL, buildMessage(header, body, keyPair))
      },