I am trying to sign and send an order request to Hyperliquid. And no matter what I try, and I tried a lot of different things, I get the response:

L1 error: User or API Wallet 0xb37035fd36b3fc08b42969b806f6d01b9edce5ff does not exist.

The Hash is always random. I assume it should show my address every time if code would do the right thing.

I watched SDK of Hyperliquid platform and tried convert their code from Python and TS to C#. Nothing helped including CGPT.

public static EthECDSASignature GetSignature<T>(string privateKey, T action,
  long nonce,
  string? vaultAddress,
  bool isMainNet = true)
{
  var bytes = EncodeLOneAction(action, nonce, vaultAddress, isMainNet);
  var signature = new EthECKey(privateKey).SignAndCalculateV(bytes);
  return signature;
}

public static byte[] EncodeLOneAction<T>(
  T action,
  long nonce,
  string? vaultAddress,
  bool isMainNet = true)
{
  var actionHash = ActionHash(action, nonce, vaultAddress);
  var domainSchema = GetDomainSchema1(actionHash, isMainNet);

  var signer = new Eip712TypedDataSigner();
  var encoder1 = signer.EncodeTypedData(domainSchema);
  
  byte[] encodedDataHash1 = Sha3Keccack.Current.CalculateHash(encoder1);
  return encodedDataHash1;
}

private static byte[] ActionHash<T>(T action, long nonce, string? vaultAddress)
{
  var data = MessagePackSerializer.Serialize(action);
  var nonceBytes = BitConverter.GetBytes(nonce);
  
  data = [.. data, .. nonceBytes];
  if (string.IsNullOrEmpty(vaultAddress))
  {
    // Add end byte
    data = [.. data, .. new byte[] { 0x00 }];
  }
  else
  {
    // Add new line byte before adding address
    data = [.. data, .. new byte[] { 0x01 }, .. AddressToBytes(vaultAddress)];
  }

  return Sha3Keccack.Current.CalculateHash(data);
}

private static TypedData<Domain> GetDomainSchema1(byte[] hash, bool isMainNet)
{
  var typedData = new TypedData<Domain>()
  {
    Domain = new Domain
    {
      ChainId = 1337,
      Name = "Exchange",
      VerifyingContract = "0x0000000000000000000000000000000000000000",
      Version = "1"
    },
    PrimaryType = "Agent",
    Types = MemberDescriptionFactory.GetTypesMemberDescription(typeof(Domain), typeof(AgentType))
  };
  typedData.SetMessage(new AgentType
  {
    Source = (isMainNet ? "a" : "b"),
    ConnectionId = hash
  });

  return typedData;
}

[Struct("Agent")]
private class AgentType
{
  [Parameter("string", "source", 1)]
  public virtual string Source { get; set; } = null!;

  [Parameter("bytes32", "connectionId", 2)]
  public virtual byte[] ConnectionId { get; set; } = null!;
}

My serialized post request after all the jazz before sending to Hyperliquid looks like this

{
    "method": "post",
    "id": 0,
    "request":
    {
        "type": "action",
        "payload":
        {
            "action":
            {
                "type": "order",
                "orders": [
                {
                    "a": 1,
                    "b": true,
                    "p": "0.2",
                    "s": "1100",
                    "r": false,
                    "t":
                    {
                        "limit":
                        {
                            "tif": "Gtc"
                        }
                    }
                }],
                "grouping": "na"
            },
            "nonce": 1726578116356,
            "signature":
            {
                "r": "***a6d70929151805870921825f219",
                "s": "***d3090bb540e015a69226a35ae8d",
                "v": 28
            }
        }
    }
}

At this point I am completely out of ideas what could be wrong and asking for help.