title: Erdpy: Token issuance transaction fails with code: internal_issue
body: <p>I try to make an ESDT token issuance transaction using the following Python code</p>
  <pre class="lang-py prettyprint-override"><code>from erdpy.accounts import Account, Address
  from erdpy.proxy import ElrondProxy
  from erdpy.transactions import BunchOfTransactions
  from erdpy.transactions import Transaction
  from erdpy.wallet import signing
  
  
  TOKEN_NAME = b&quot;Cowdings&quot;
  TOKEN_SYMBOL = b&quot;MOO&quot;
  
  DECIMALS = 18
  SUPPLY = 1000 * 10**DECIMALS
  
  
  def hex_string(s: str) -&gt; str:
      assert type(s) == bytes, &quot;Make sure everything is bytes data or utf-8 encoded&quot;
      return hexlify(s).decode(&quot;ascii&quot;)
  
  
  def hex_int(i: int) -&gt; str:
      assert type(i) == int, &quot;Make sure everything is bytes data or utf-8 encoded&quot;
      return hex(i)[2:]
  
  
  proxy = ElrondProxy(&quot;https://devnet-gateway.elrond.com&quot;)
  sender = Account(pem_file=&quot;test-wallet.pem&quot;)
  sender.sync_nonce(proxy)
  
  tx = Transaction()
  tx.nonce = sender.nonce
  tx.value = str(0.05 * 10**18)  # 0.05 EGLD, as required for issuing a token according to the documentation
  tx.sender = sender.address.bech32()
  # System contract address to issue out the new token as per
  # https://docs.elrond.com/developers/esdt-tokens/#issuance-of-fungible-esdt-tokens
  tx.receiver = &quot;erd1qqqqqqqqqqqqqqqpqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqzllls8a5w6u&quot;
  tx.gasPrice = 1000000000
  tx.gasLimit = 50000
  tx.data = f&quot;issue&quot; \
            f&quot;@{hex_string(TOKEN_NAME)}&quot; \
            f&quot;@{hex_string(TOKEN_SYMBOL)}&quot; \
            f&quot;@{hex_int(SUPPLY)}&quot; \
            f&quot;@{hex_int(DECIMALS)}&quot; 
  
  tx.chainID = &quot;D&quot;  # For devnet https://devnet-gateway.elrond.com/network/config
  tx.version = 1
  
  tx.signature = signing.sign_transaction(tx, sender)
  tx.send(proxy)
  </code></pre>
  <p>It fails with</p>
  <pre><code>ProxyRequestError: Proxy request error for url [https://devnet-gateway.elrond.com/transaction/send]: 
  {
      'data': None, 
      'error': 'transaction generation failed: invalid value', 
      'code': 'internal_issue'
  }
  </code></pre>